Yes, and in case of other plug-ins (Shave, Yeti, RMS, etc…) you also have to remove several entries in PreRenderMel, PostRenderMel, etc…
And also scriptNodes, which create scriptJobs (fortunately it’s not very often).
Some plug-ins add so much hidden things (not “unknown nodes”) that a mel command is provided to remove everything :
For RMS : rmanPurgePlugin
For Shave : shavePurge
In case you use maya reference files, you obviously have to “clean” the deepest maya files, then go upper each time.