I was married in Aruba in July 2011. I also had my heart set on having my Aruba DW at an all-inclusive. After doing on line research, I chose 4 resorts to visit in April 2010. I ended up choosing the Divi/Tamerijn All-Inclusive, but the Occidental was a VERY close second. I stayed in Aruba for my honeymoon, and moved to the Westin, which is next door to the RIU. So I don't have direct wedding experience with either resort, but here are my observations.
The Occidental is really beautiful, inside and outside. I was stunned by the pool. It sort of looks like a lagoon: curvy shape, lots of trees and vegetation around it, waterfall in the middle, a foot bridge to a tiny island in the middle (where the water fall is). When I visited, there were canopied bed/couches that I really liked because I can't be in the sun ALL day long. I thought the beach area felt a little crowded and claustrophobic. Like all the high rise resort beaches, there are rows of palapas (thatched, permanent umbrellas). But then there were also lots of palm trees planed between the palapas. (Check out the satellite view on Google Maps to see for yourself). As for the ceremony site, I thought was very pretty - right along the water. The reception could be held in 1 of 2 places: in a little opening on the sand, nestled between an alcove of trees and the first row of palapas closest to the hotel, or somewhere around the pool. I liked the cozy, semi-hidden feeling of the sand location.
I know less about the Ru's wedding accommodations, since I never made an appointment with the resort's wedding planner. What I can say is that it's HUGE. The white palace-looking building was the most recognizable along the Palm Beach coast line when we were at sea on a snorkeling tour. It's both wide, covering a longer stretch of beach, and deep. I think this would probably make the beach feel less claustrophobic. They have multiple pools. I think it would be less monotonous to be able to hang out in different areas of the resort. I planned multiple excursions during the honeymoon portion of my stay on the island, so I only spent about 50% of my time at the resort. But if you're the kind of person who liked to just unwind and vegetate at the resort, you may appreciate a larger one.
Hope this helps at least a little! Good luck in your planning!