Well they did say read at your own risk!
More for the benefit of newer players who read this, if a teammate asks you for an engineer, you aren't obliged to provide it (although it's often a good idea since what also often happens, as described here, is they can get very angry about not receiving the engineer). If they then ctrl-K their ACU in response to your refusal (as described here) they're breaching the FAF rules and you can report them.
The above is a big reason why for a long time I liked playing Astro craters out of the 3 maps that seemed to be played on FAF (Setons, Gap, Astro), since at the time 4v4 TMM wasn't a thing and I really dislike maps where your team expects/demands you to play a particular way and you dont have the freedom to experiment with your own battle plans.
Fortunately now I have TMM and while a few maps there might be an expected air or navy slot it's fairly rare to get pings as described in the OP.
I can't speak to the role-designating (I do play Gap but generally try to avoid it as it's too stale for me) beyond that there are some cases where if everyone is expecting you to focus say on air units because you're in the most protected slot, and you then flaunt their requests and leave the team with no air, they will justly be quite upset, but as far as sharing engineers and the like goes, I'm not sure it's a good idea to encourage people to be uncommunicative assholes and work against their team, just because it's not technically against the rules... I have played too many games with people "just doing their own thing" that happened to involve entirely ignoring teammates, communication, and the general situation of the game (who sometimes then have the sheer gall to call you "toxic" for being vehemently displeased with such infantile behavior).