I have been working on a humor and satire site that I built with Yola. It has a character blog attached. I've been posting to this blog frequently lately. It definitely gets indexed pretty quickly, though not immediately. I've ben getting some decent search engine traffic to it, mainly from topical keywords.
My blog doesn't yet have oodles of content up there, although it's about a year old now I think. I also haven't done much link building to it.
Considering these factors it seems that Yola has very good all round SEO. So that's another positive to add to what is surely one of the most elegant and customizable free website builders out there.