Hey mate let me start by saying I honestly don't know for sure but my experience is Padang doesn't have a surf focus or culture it's just another busy Indo city.
My experiences on Sipora is that everything is focussed on prone surfing and there's not much sup surfing. Take my own boards so haven't needed to consider rentals.
Apparently Telos and Banyaks are more suited to supsurf but you'd have to fly out of Medan.
Once again pure conjecture but a rental company would more likely focus on rich flat water paddlers than reef rippers surfers. FWIW I travel with a prone and sup in an 8'3" bag with wheels and its doable but theirs lots of transfers between plasnes, boats, cars and bikes-the whole shebang makes it hard yards-and the ments are worth it. Hope you have a good trip