I'd suspect so, but I'm not sure that would necessarily be true with all equipment. Try it and see. If you get continuity to one of the xlr pins, you've verified that that pin is ground. If you don't get continuity to any pins, then that approach won't provide you with an answer. Same goes for measuring to chassis.
By "continuity" I mean something very close to 0 ohms (or at most say 1 or 2 ohms), as measured on an ohmmeter, not just an indication from a buzzer or other rough continuity checker which could indicate continuity even if a significant resistance is present.
Also, when you measure it would be prudent to have all signal cables from other pieces of equipment disconnected from the amp, so that your measurement is not confused by any possible paths to ground through the other equipment.
Regards,
-- Al