Can these be using in conjunction with a uv lamp?

Certainly; although you might consider the flow rate of the lamp;
if the pump exceeds it, build a manifold (an array of valves) where
only one of them goes to the uv lamp.

Also, we were considering a waterfall (not huge), but the lift is about 4.5
feet.. can they handle that?

Yes.

A concern I'm having, is how much constant water agitation we might end up
with.. the spitter, the bubblers, and now this as well.

Not all water movement has to go into a water feature.

In your manifold, you can return some water directly to the pond, just
below the surface. This will be helpful to your pond if your water source
is at or near the bottom of your pond.

Example:

Pump--Tee--Array of valves--1 fountain, 2 water fall, 3 back to pond

A picture is he

http://www.aquaticeco.com/index.cfm/.../8341/cid/2034

You can make these out of cheap parts from Home Depot.

C//