Are these suppressors regulated at all?
Yes and no.
A
detachable suppressor for an airgun is an NFA taxed/regulated item the same as it is for a firearm. The existence of .17 caliber firearms makes even a .177 caliber suppressor "readily convertible".
An airgun (paintball or Airsoft too...) can have a suppressor if it's
permanently integral to the barrel and action and then it's a non-NFA item. That's why the Gamo can have the expansion chamber and baffles.
However, I think the ATF might start making trouble if an integral airgun suppressor started working "too well", and they feared people would start cutting them off and trying to thread them etc. Most airgun makers who go for some suppression will go with a barrel shroud and an expansion space with no baffles to stay on the right side of things.