[sibrahim]

That's certainly been my experience.

I've had arXiv automatically block bare uploads of TeX-derived PDFs (presumably identified through PDF metadata). For these, it required that the source be uploaded and compiled on their server.

On balance, it's probably best to require source as arXiv does, but this can create interesting issues from time to time. Since the source is downloadable, researchers can inadvertently end up sharing partial results or snark that was commented out in the TeX source.