Jobroller is also a theme and so it will override your existing theme. One workaround is to install wordpress-jobroller on the subdomain and just make a menu link on it on your main site. In that way your main theme design will remain.
Please help our moderating team work more efficiently by not sending us support questions via PM. You can read more about how AppThemes support works here. However, you can send a PM to follow up and remind me if I missed your support request/thread.
