Noting: Premade loops not allowed, but samples/sfx are--if I have drumloops that I have the legal right to use, and then chop/rearrange them into things (e.g. kick or hat samples)--is this OK?
Hi! The rule's intention is to prevent people from using loops and sample packs with the intent of writing music for them, e.g. just dragging and dropping loops and call it a day. In the past, there have been people using loops in their submission as well, but it was minor and the majority of their work was still their own composition and arrangement. So I'd say yes you can use them, as long as the majority of the work is still your own composition and arrangement. For sure, it'd be better if you can record the instruments by yourself, but I understand that there are a lot of people (including myself) who don't have access to and can't play such instruments. Hope this helps! ^^
(This also goes the same with other instruments, not just drums!)