I would like to know if its possible with the new source control possibilities since 8.5.3 if we could use Rational Jazz as the source control environment.
Yes, but not as integrated as you want it to be. First import your Domino project into RTC by using Project Explorer, right click/Import. Choose "File system" and specify the location of your On-Disk project. Then you can upload your code into an existing repository workspace.
So you will still have to use the Rational user interface for source code control.
I noticed that "see pending changes" wont work as expected in RTC3.0.1. It will take some seconds before a refresh has any effect. So if you cant see your changes in RTC, wait a few seconds, then hit refresh.
Reminder to self: should create a blog post about using RTC with Domino Designer