Of course it's possible, but what's the point, if parties want to transact in a different currencies?Is it impossible to fix price in BTC and automatically index price in Dash based on an average API call from a few exchanges?
For Alice to pay in Dash and Bob receive BTC, there should be a Carol, that would take Dash and send BTC. For Bob paying in BTC and Alice receiving Dash only, there should be a Carol, that would take BTC and send out Dash. You can't remove Carol otherwise, but prohibiting Alice and Bob to transact. And by removing their ability to transact, you will kill at least 99% of transactions. Thus Dash-only version of OB would be dead on arrival.
I understand your idea of not wanting to fund integration with Carol out of Dash funds. Problem is that every other currency community would think the same way. So, the fastest way to get Dash in the OB is to get Carol, I mean shapeshift or openbazaar to fund this integration. As soon as I'll get a free minute, I'll contact them, though I doubt that a cold contact would work.