Just thought I would post a quick update in this. Since I posted this review, I've sold my MP5SD and my Surefire 628 (along with a lot of other things).
That left me with my Omega OM9 and the B&T (since unlike the 628, there isn't much market for a used B&T, as they can be found pretty cheap brand new).
With some finagling, I actually got the B&T mount to fit properly on the Omega. It just took a little bit of work to force it on and it works perfectly.
I can say that, while I still prefer 628 in terms of how it feels and control placement, I can now say with certainty that you absolutely can use a suppressor with the 3-lug with the B&T mount on it. I can put my Silencerco Hybrid with the 3-lug adapter on the gun with no issue with the B&T in place. So definitely +1 to B&T for that part of the design. I just wish they made their grip a bit more ergonomic.