I used to sell and repair phones, for a number of years. Honestly it's a case-by-case basis, sometimes you'll be fine and they'll fix it no issues (like your example, I've seen that plenty of times, and I'd expect the Nexus line to have that happen more often)... but sometimes the vendors will just refuse. That's why the unlock screen says "may void your warranty". So, it's not completely cut-and-dried, but you'll have a much better chance of it with the Nexus line, in my experience (and yours!).