We're having our wedding at the Royalton Riviera Cancun which does have a small waterpark. I also wanted to offer some feedback on the Memories resort!
My friend got married at the Royalton Punta Cana which shares a beach and amenities with the Memories Splash. We personally stayed on the Memories side, however all of the other guests stayed at Royalton.
I would personally book my wedding with Royalton Punta Cana, if a waterpark is a must. Their waterpark is actually quite impressive as a resort property. Guests who want a cheaper alternative could book wtih Memories and still attend your wedding! With Royalton, you get all of the amenities from the memories, but also get all of the amenities from the Royalton side. Way more choices for meals, and access to all of the pool & beach bars, closest to the beach!
The only downside to the wedding location, is that the location on the beach is not that private. They do have a secluded garden space that I feel would be gorgeous for a wedding!
Let me know if you want any other feedback about the memories/royalton, I'll be happy to help!