As you have noted, it is the InstallValidate action that determines whether a FileInUse dialog is presented to the user. This information is documented in the windows installer SDK help file, meaning that it is part of the windows installer service and the "standard" actions that you find in any MSI.
It is perfectly possible that the Wise template includes additional functionality in this area, but I don't have any information that would confirm (or otherwise) whether removing the FileInUse dialog from the MSI would avoid windows installer showing one anyway. Unless another forum member can advise you from personal experience, the quickest way to check this would be to actually give it a try and see what happens.

I have no clue how to "force" suppressing of the FilesInUse dialog however; if you for example use the "/qb-" switch where "-" will suppress any modal dialog the FilesInUse dialog shouldn't get displayed.

The FileInUse dialog is actually a Windows Installer dialog that is triggered if a file is in use.  The option to kill the file in use before the file is to be replaced is always an option to prevent this dialog from appearing at all.  There is an article in our KB 17128, that explains how to this dialog works, and what you can do to modify this dialog.  I hope this information is helpful.

KB 1728

Listed below is the help from the SDK below that gives some good information (in the paragraph that starts "The InstallValidate action queries") about making changes to that dialog.

The dialogs used in the product are Windows Installer dialogs.

You may also want to consider killing the application with the Application Kill WiseScript located in the Samples directory at WPS\Wise Package Studio\WiseScript Editor\Samples.

From the SDK:

FilesInUse Dialog

A FilesInUse dialog alerts the user of processes currently running files that must be overwritten or deleted by the installation. This gives the user the opportunity to shut down these processes and avoid having to reboot the computer to complete the replacement or deletion of these files. See System Reboots.

This dialog will be created as required by the InstallValidate action.

An entry is added to an internal FilesInUse table if any file is overwritten or removed while it is open for execution or modification by any process during file costing. The FilesInUse table contains columns for the name and full path of the file. When the InstallValidate action executes, the installer queries the FilesInUse table for entries and determines the name of the process using the file. The InstallValidate action adds one record to the ListBox user interface table for each unique process identified by this query. The record contains the following values in each column:

Property: FileInUseProcess
Value: <Name of process>
Text: <Text contained in the caption of the main window of the process>

The InstallValidate action then displays the FilesInUse dialog. This dialog displays the processes that must be shut down to avoid the requirement of restarting the system to replace files in use.

The InstallValidate action queries the Dialog table for an authored dialog box with the reserved name FilesInUse dialog and displays it. This dialog must contain a ListBox control that is tied to a property named FileInUseProcess. By convention, this dialog has an Exit, Retry, or Ignore button, but this is up to the UI author. Each button should be tied to an EndDialog ControlEvent in the ControlEvent table. The InstallValidate action responds as follows to the value returned by the DoAction ControlEvent, as dictated by one of these EndDialog arguments associated with the button pushed by the user:

Retry: All values added to the ListBox table are cleared, and the entire file costing procedure is repeated, rechecking for files that are still in use. If one or more processes are still identified as using files to be overwritten or deleted, the process repeats; otherwise, InstallValidate returns control to the installer with a status of msiDoActionStatusSuccess.

Exit: The InstallValidate action immediately returns control to the installer with a status of msiDoActionStatusUserExit. This terminates the installation.

Any other return value: The InstallValidate action immediately returns control to the installer with a status of msiDoActionStatusSuccess. In this case, since one or more files are still in use, the subsequent InstallFiles and/or InstallAdminPackage actions must schedule the in-use file(s) to be replaced or deleted when the system is restarted.

If there is no ListBox table in the database, InstallValidate exits silently without an error.

The semicolon is the list delimiter for transforms, sources, and patches, and should not be used in these file names or paths.

Files marked read-only in a read-only location are never considered in use by the installed.

Thanks for information

But what will happen if there is no FileInUse Dialog in MSI?

How the process goes in that case?

...[quote]the quickest way to check this would be to actually give it a try and see what happens.[/quote]