flame seal not req by code

I actually think that might be true, but I can't confirm that. I seem to remember a max gap between the box and the gypsum, above which you had to use fire caulk or similar intumescent seal. The use of rated device boxes in fire rated assemblies is covered under the UL Orange Book, of which I do not own a copy. It's actually a 2 volume expensive affair. The NEC is mute on the matter.

I know in this are the only time I have had to worry about sealing is in the hospitals and restraunts. They want the boxes wraped, penitrations sealed, and boxes sealed between the drywall on every firewall. Most of them even spec the Hilti products.

I have seen it used on common walls in condos and aptments.

Fire Resistance Penetrations

There seems to be a lot of confusion with the need for "fire caulking" and penetration sealing for fire resistive locations.
If one is talking about 1 & 2 family dwellings, there are very few locations in a dwelling that require fire caulk. Most dwellings will only require fire caulking where the garage is located adjacent to living space and the walls/ceilings of a boiler room. The rest of the locations in a dwelling are not listed as fire assemblies, therefore those locations will only require "draftstopping". Draftstopping can be performed in many different ways, and is a lot less expensive than firestopping.