First of all, failure of that point of attachment isn't a big deal, right? Worst case scenario is that you lose the $7 bolt-snap on a dive. The more likely scenario, if the attachment of the bolt-snap fails, is that it will probably stay clipped to your D-ring and you may have to search a little to locate your SPG. No big deal for part of one dive.
Lots of simple brass-and-glass SPGs don't have a convenient "loop" to attach a bolt-snap or double-ender. That's why people lash the eye of a bolt-snap (using bungee or caveline) to where the SPG connects to the HP hose.
Theoretically, you could use a short double-ender for that connection, but the gate used to clip off to the D-ring won't be able to spin freely. This may make clipping/unclipping more difficult. Note that I said a "short" double-ender because if it's too long...it makes clipping/unclipping more difficult. Try it and you'll see what I mean.
FWIW, you don't need to have a BP/W setup to fashion a clip for the SPG in this manner. It works just as well with a conventional jacket BCD.