When running Connect from source no plugins are loaded by default. You will need to install and add them separately. We just opened up the repository containing the Nuke plugin and you can find it here: https://bitbucket.org/ftrack/ftrack-connect-nuke
We're currently working on documentation for how to run them from source and not from a built package. I'll update this thread when I have the complete steps needed to make it run.
Note: Bitbucket seem to have some problems with their web site at the moment.