Yeah, that's exactly what my Muay Thai trainer did. I would go to him twice or three times a week for my stand-up and then the other days with the other guy I would train primarily ground fighting. It's brilliant, convenient and easy on the bank account.
I took Shotokan (which is a form of Karate) and a guy who has sparred with Chuck Lidell came in to do some MMA classes with our class. He taught us some Brazilian Jujitsu stuff and also some wrestling takedowns as well as some submission moves.
Next year I will try to get involved in some submission wrestling since me and some guys have been doing it on a regular basis after school and I don't seem too bad considering I'm usually the underdog because they're all bigger then me. I also want to do some Judo later in life.