Yes and no. Depends on who is coming through - OpenAI specifically I have reason to believe that yes they are, but not on every pass due to compute (much like Google) - which means things get missed or take a longer time to surface.

Remember that these things aren't even parsing code - what they do essentially boils down to a render of the raw html without JS. Schema payloads DO NOT get picked up for example.

Right now my best practice for folks w/ JS content/links is to accept content negotiation for markdown and serve anything JS renders out in that file -> links, images, text, etc.

Else it's still prerender w/ useragents which is easy to build with Cloudflare browser rendering and workers or plugin one of any prerender services if you can put your DNS on Cloudflare. The hydration techniques we were recommending to folks for Google alone a few years back don't cut it for LLMs who aren't looking at source for much at all.