I’ve asked that question in a dozen MMO forums and I’ve never gotten an official response from a developer/moderator. It is highly unusual for them to comment on anything to do with cheat detection as they could unintentionally reveal something critical to cheat developers. If they did actually comment directly it would probably just be a generic reference to a line in the EULA about not modifying game files.
I’ve used it without issue in dozens of games (including several recent MMO). The SMAA “injector” name is a bit of a misnomer as it doesn’t actually “inject” anything in the sense that cheat tools do.
The FXAA shader they are using in GW2 is awful (soooo much blurring) so its well worth the risk to me, personally.