You shouldn't have any problems with mixed versions of Open Access assemblies, because our references are to the binaries included in the Sitefinity package.
Can you elaborate more about your scenario? When the problem appears: on development or runtime?
You already got an answer about the ORM license:
Yes, you have to separately install the Q3 Open Access from here. Note that this is the trial download which will work OK with Sitefinity since we are distributing all necessary binaries and executable in the Libraries folder of your Sitefinity SDK installation. Therefore, you will need the installation only for the Visual Studio Extensions.
Please let us know if you have additional questions.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!