I don't have a registered machine gun receiver (sigh), but I can help a bit with this and your other question.
My Glock-lower is technically Runner Runner Guns, but it's the C-9 Stripped Billet Lower Receiver built by New Frontier Armory, and marketed by them, RRG, and JobBob's (as the Spartan) and probably others. In its standard form, it does not have a LRBHO. You have to get a special upper with LRBHO capability, and to be honest, it's a bit of a Rube Goldberg affair. According to NFA: "Due to the force exerted on the BCG with a blow back system, there is a high likely hood of breaking the bolt catch when activated by the LRBHO feature." I never pursued it, because it didn't seem important.
The "9mm hammer" is a hold over from the days of "ramped" and "non-ramped" bolts. Virtually every 9mm bolt you could even find these days is ramped. I don't know where you'd find a non-ramped bolt. In the days of non-ramped bolts, you had to worry about a specific hammer contoured to withstand the hit from the bolt.
My Glock-lower AR runs like a sewing machine, with both my 9mm upper and my .40S&W upper. I highly recommend them as a PCC option. Feel free to ask anything else, or on your next swing through SoNH, come shoot it.
ETA: I also have a Colt-compatible 9mm SBR, which I was shooting this weekend, and it reminded me how much I like that platform, too. It uses the standard AR BHO, and the look with straight mags is just...better. I'm running a Spike's 9mm buffer in my Glock-lower AR, but have switched to an Armspec captured 9mm recoil system in my Colt-lower. It seems smoother than the Spike's version, but maybe that's just confirmation bias on my part.