Have been using SF and SONAR in tandem for many years.
With the ability to send a clip, track, section of audio or multiple tracks from SONAR to SF, edit them and then send the processed audio back to SONAR, there is no real need to use SF plugins in SONAR but SF 10 and SONAR can share the above plugins as stated. I use a free wrapper called FX Chainer which works well for using 32 bit DX/i in SONAR x64 but its no longer available for download.
Vegas 12 has gone full 64 bit and I expect SF 11 to go full 64 bit. Although I have to say I've never had an audio project I couldn't load in SF. that's either a stereo or multi track project.