What do you mean by "remote snippet of html"? An iframe loads whatever's on the other end of the src URL. If that's a "whole page", then it loads a whole page. If it's just a "snippet" of content, then it loads that. Any snippet you think of can be loaded by iframe exactly as described. The only hitch, really, is that it's always treated as block-level content instead of CSS-style "inline" flow-level content, but that's clearly not relevant to the use case at hand—embedded tweets are already block-level.

It's not clear what you're asking for. (E.g. do you want that snippet not to be sandboxed?)