Hi Ruben
We've have configured all our existing 6.9 deployment servers as site servers as part of our migration to 7.1. As long as your servers meet the minimum requirements(IIS, .NET etc) it should work. We havent been using the DS Web Console so cannot comment if that will cause any issue.
We've installed Package, OOB & Task site services but haven't yet rolled out the deployment solution site server componenents yet though. I'm assuming the PXE services included in the deployment site services will conflict with the existing 6.9 services therefore we wont be rolling out the deployment site servers until we have migrated all our images etc onto 7.1 and are ready to replace the DS 6.9 PXE service with the 7.1 PXE service.
Cheers
Kevin