1996 EJ22: Different looking water pump??

At various times, Subaru has made water pumps with both types of impellers shown in your pictures. On my 97OBW, the impellers on both the factory original and the replacement OEM WP I bought from a Subaru dealer look like the rebuilt one you bought, so I'd say you're good to go with it.

The impeller on the reman you bought is actually a more efficiant design than the one you removed. The open impeller allows coolant to spill out of the blades resulting in decreased flow.

Thanks very much, gentlemen. Maybe I can wrap this project up today.

Both types are available under two different Subaru part numbers. The open-style impeller was introduced with the original 2.5 l engine, if memory serves. In the aftermarket, both types are also available and considered fully interchangeable.
By the way, the removed pump was not original to the car because it was installed with RTV sealant. What did you pay for the re-manufactured unit? Chances are, one could get a new one through eBay/RockAuto/Amazon etc. at about the same price.