I wouldn't blow it. Degreaser is fine, so is spraying it off with a garden hose, but if you're using air to blow it, you can push the degreaser past the different seals and that wouldn't be good.
Every year before annuals we pressure wash the underside of the buses with a hotsy. That water will be close to boiling and the grease and grime just falls off like nothing. I did it once without the hot part on, and you could definitely tell a difference in efficiency. After washing, we'll then grease everything and go through and inspect it.