I have not used our libraries in an SSIS Script Task, but I have found this helpful resource online for accessing custom .NET assemblies in SSIS Script Tasks. Please let me know if you don't find this helpful, or if you have any questions.
I get an error "No Template Available" when adding the reference. The assemblies are usable until the script task is closed and reopened, then they have lost thier reference.
I did some digging, and I was able to find a string of people having similar errors, while using both custom and standard assemblies. I found this site after some time, and it seems as though he was able to get them installed and lists his method.
Again, let me know if this isn't helpful, and I'll try to find some good references to the problem.
I have SSIS working with the dll's & the scripts, and yes it took a little tweaking. Further I think that at first working with the DLL's during dev will hinder comprehending how the API works, and now that a unified set of cs scripts are available, I suggest using those for dev then switch to the DLL's in alpha and beta builds/testing and deal with any remaining issues then.
It's been a couple of weeks so I'm not remembering what the errors were and their solutions, but it's enough to say I have it working with the DLL's in Sql Server 2008 r2 developer edition.
And now in WPF (.Net 4x)