I had friends that matched into good DO programs with 500's on their COMLEX I. This has been posted 100 times, but DO programs care a lot about your rotation there. There are very few programs that have 600 cutoffs and this generally applies to non-rotaters. 600 gets you in the door at most places. 500 will not kill you unless you 1. tank step II or 2. are a tool.
Step II is becoming more important in the DO world for ortho...people have been burned by dropping a significant amount from their step I. Seems more of a "can hurt you more than it can help you" type of thing.