As per our understanding, the values displayed in the Resource Type dropdown are according to the resource types present in SMP and while executing the project each time would create a new resource of its type. We didn’t find any option to select resource type with process variable.
In other case, if User wants to create a new resource in SMP component in Symantec Workflow to create new assets then by passing certain name/other properties for Resource ,user can avoid duplication while creating new resource in existing resource types.