Let me address this; I'm an IMG and am well familiar with the very silly DO versus allo arguement because in the IMG world it comes up quite a bit.
First of all- outside electives for IMGs ARE credited in most states but there are exceptions (PA?)
The reason its harder for DOs that US allopaths is for the same reason its harder for IMGs: the reality is that most DOs take that route because they didn't get into a US allopathic school. While there are exceptions, this is a general truth and even if you are an exception, the assumption is potentially against you. Plus of course there are more MD's applying than DOs so there is tha issue.
Does this mean you can't make it? Of course not. There are DOs in the field and will continue to be so. An excellent applicant is an excellent applicant and coming from a DO school shouldn't be a catagorical ding against you. Indeed I'd say that coming from a DO school and one of the better IMG schools will give you a chance.
To optimize this chance, I would do some outside roations, really excell at them. Also, try to get involved in research. Show dedication and aptitude now to the field. And stay in contact with program directors from programs that you connect with. if you're good, you may need to show yourself a little more, but you can do that.
Steph.