I found out by accident that you can use your pool cup at other hotels. We were staying at Royal Pacific and decided to pool hop over to Sapphire Falls-when I ordered a drink I had my room key and the bartender asked if I had a pool cup from there. I said yes, but I didn't bring it with me. She said that's ok, I can still give you the refill discount! Awesome!!
Cabana Bay has their own style pool cup so you cannot use another hotels cup for refills there. I have however brought back my CB cup from prior trips and received the refill price-even though it's a different style now.
Also, when I was there in June, Hard Rock Hotel has since done away with the refill pricing.....1 price period, so other hotel cups will not work there anymore.
also, on a side note, my last trip at Royal Pacific-instead of refilling my pool cup they just kept giving us new ones (at the discounted price). We spent most of the day at the pool and ended up with like 6-7 cups by our loungers! (no idea why they didn't take the dirty ones away) LOL