is there any uncompatibility between Joomla template of yours and the componant so called Community builder? and more precisely for Nexus and Solar sentinel templates?
Community Builder, as with any other 3rd party extension should function properly with any RT template.
Functioning as far as operating with the Joomla core code.
(Remember, a template just changes the way things look, not how they operate, much like changing the color of the paint on your car doesn't change the way the engine or transmission work.)
From template to template, you may need to make some css changes to make everything 'look right'.
We can't test every template with every extension (close to 5000 are currently available).
So, your best bet it to install and test it yourself, and post in the proper template specific forum if you have a problem.