Simply ask the suppressor manufacturer. In general, stainless steel suppressors are perfectly fine for ultrasonic cleaning. You're not going to hurt them at all by putting them in the ultrasonic cleaner. You're really gonna have to rinse it out well, because of all the crap that gets trapped in the baffle system.
For the most part, rifle suppressors really don't need to be cleaned. But I understand the desire to do so.
Also, look into "The Dip" used for automotive parts. Works well on carbon and other deposits. I wouldn't use it in an ultrasonic cleaner, however. That stuff stinks as well.