Is it okay to wear flip-flops or is certain footwear required?

Wear water shoes

Watershoes

If the flip-flops have a back strap to hold them on then I'd say it's probably ok, but I suggest sneakers or water shoes

Flip flops do not give you much traction in the raft and are not ideal for walking to and from the raft. Water shoes or sandals are much better. Sturdy footwear is required on more aggressive trips.

you won't be allowed to wear flip flops. if you don't want to spend money on water shoes, just wear some old sneakers.

You need closed toe shoes. They have wet suit shoes there if you need them.

I would not. If you end up in the water there are lots of sharp rocks. Flip flops are easily swept off your feet and lost

Flip flops with backstraps are ok. If you are planning to take a dip then watershoes or sneakers are recommended.