Yes I've personally come across two different GM's on 3 total occasions, that were monitoring camps in both Mistmoore and Solb. Technically, there was a 4th time I saw a GM, but that was because they were doing an GM event, which is kind of unrelated to what you are asking.
Yes. Several times. A dev (niente) once, too. They gave me cookies twice and a super OP regen buff. I've also participated in a GM "event" (bring me 4 different poison glands) once that resulted in a cosmetic weapon aug, and guildmates have talked about two other GM "events." You spend all of your playtime locked in LGuk or CL then complain you never see anyone other than Guk scum and tunnel turds.
i met one on Aradune when i still played. he liked my transmog and gave me some wand clickys that were bugged
After 21 years.. yeah I've seen and talked to numerous GM's and Guides, participated in one-time Server events and sat down in a mostly deserted zone and had a real conversation with a few. Granted this was multiple years ago when every server had at least one full time GM or Senior Guide on it. I still remember when Sal'Varae (yes that's where the robe got it's name) was a main server GM and would pop on E'ci from time to time running impromptu "events". Granted this was back when the folks in charge actually still gave a damn about the game and it's player base rather than how much they made off the Marketplace this week. (My opinion)
I've been listening to some ex-GM talks about this stuff on Twitch. They really loved doing those events, but they had to finish up their queue and then they could pick from a list of events. I miss stuff like that.
Yeah one is on a couple of our raid logs when we were doing Sky. No idea why they were there! they followed us around, then left after a while. Didn't even give us cake... When I have needed to speak to one or whatever they've been pretty good though.