..I think this is also partially because the locals likely wouldn't be particularly happy about aliens, and while it's not like the Garenhulders could do a damn thing about it (unless/until they train their asses off until their power levels are over a billion and throw off their Saiyan overlords).By that logic, they could just drop the masquerade altogether and introduce themselves as aliens, because the Garenhulders don't know what Saiyans are, can't do anything about it, and aren't likely to go into space. Obviously, they've instead decided that even letting the Garenhulders observe identifying information is too dangerous, possibly in case some alien scouting mission comes along and interacts with the locals. The name, "Gohan", is extremely identifying information, possibly even more so than just being a race of humanoids with tails.
I also don't think the Masquerade is for a scouting party as much as for a fully fledged invasion (which would be noticed)/peaceful contact with the galaxy at large, not to mention that discovery of aliens is very likely to get the the Garenhulders to try to get out into space, unless we forcibly prevent them from doing so or tell them why they shouldn't (in which case any individual Garenhulder might be able to cause the destruction of the Saiyan race if they got into contact with aliens).
Perhaps it's because they kept their names secret since they were unusual at the time of their arrival, and since they never used their Saiyan names in public they never changed the naming conventions? Not to mention that many hybrids (not sure if they should be called Saiyans until Lady Garla united them) might have genuinely taken on Garenhuldian (not sure what the correct adjective is) names as their only names and only started to take on Saiyan and/or Earthling names after Lady Garla unified the Saiyans.There is a reason that they use different names for their masques. They've been around for hundreds of years, since the times when the locals were at a medieval level of society, and more than enough time to change the naming conventions of the locals until they were uninteresting. They chose to keep them secret instead. The very fact that it is unusual to her makes it more likely that Maya will find it salient and memorable, especially during this extremely emotional flashbulb memory.
In addition to that, there's only about three hundred thousand Saiyans while there's 13 billion Garenhulders on the planet, the Saiyans wouldn't be able to do squat to change the naming conventions unless they abolished the masquerade, took over the world and forcible gave everyone Saiyan names.