wprealty.org is the only place I know that does all rets/idx/mls with wordpress - they can pretty much do anything with wordpress every type of feed....all with dynamic listing titles meta-description - and even the urls can be custom structured. I know for a fact that they also do ARMLS RETS because I just got a live demo of a production site they are working on for a phoenix customer.

I think from a seo perspective one of the other things that interested me most was their use of adding "other similar listings" to a listing details page that can display 1 thru x amount of similar listings as anchor text links in a nice and customizable search phrase type structure which is handy for getting even more listings indexed for those longtail type searches.