It's not because of the lack of DO apps, it's because direct plastics right now is the most difficult residency program to match to, and there are only around 82 spots in the entire country.
Of course, if it is an allopathic program, they are going to give preference to allopathic graduates. It is the same situation as any competitive field, such as derm or rad onc. Like I said, you should go for it and it sounds like you are well qualified, but I am just trying to give you a realistic perspective from what I have heard and researched. I think it would be naive to think that its because of the lack of DO apps. But like I said, if you love plastics, you should go for it, and don't let anyone else tell you otehrwise. You should have a realistic picture of what you're up against tho.
Best of luck