Most schools (MD & DO) don't require a letter of recommendation from professors if you have been out of school for a while, but you'll want to check with the individual schools. Usually letters of rec from employers and others associated with you in more of a professional sense or community way should suffice. If you can get the professor recs then I would do so if they will give you a good one. I would approach them asking them if they can give you a good, positive rec. If they hesitate, then by all means go elsewhere. You can't afford a bad or mediocre letter of rec.