I'm wanting to use pools as scenery, but I'm wondering if this will affect gameplay in the sense that it won't be an open ride. Has anyone else done this? And does it affect gameplay?

I don't know where the problem is, because you can build a pool complex the normal way without using it or make it peepable.
So long as you don't place the pool entrance/changing room object a pool is only a decoration.
A lot people build pools and use it as big fountains for the mainstreet, because you can cover it up with pathcovers, etc.

And it won't affect your gameplay in a bad way if you think that.
If you build a park only designwise nothing must be peepable. On the other side, peeps generate allways this amusement park atmosphere.
Empty rides, coasters, pools can look good in some way, but with peeps in, on it you get more atmosphere.

Cheleste

Thanks for the info, Cheleste! That's just what I needed to know.