I don’t think so, at least when I scroll my pixelfed feed it loads images from various domains.

(I’m the dev of Alexandrite) Officially there isn’t yet a way to self-host it without modifying the code (unless you host it on one of a few specific cloud providers like the official Alexandrite site does), but now that people are self hosting anyway I think adding support for it is going to be higher up on my priority list!

I never had considered before a few days ago that someone would host Alexandrite alongside their instance so it never occurred to me that someone might first interact with Lemmy through Alexandrite. I will definitely add registration!