Hmmm - I have to ask - When your road is plowed, does it leave a pile across the end of his road?  If so, maybe he's trying to get your attention.  If not, have you tried asking him politely to just make a pass the other way to clean it up when he's done?  You might point out that it's a safety hazard, including the possibility that it could increase the chances of someone colliding with him at the intersection due to inability to stop in time.  I can't think of any statute that specifically prohibits plowing across a private road.

Sounds like you are handling it appropriately.  A agree that it's better to avoid stirring things up over a small issue - he is, after all, a neighbor, and you will have to live with each other.  On the other hand, where there are safety concerns, it sound like you do need to do something about it.  I'd still try the polite approach first, i.e. tell him it's becoming a safety issue and ask if there is some problem you are unaware of that needs to be taken care of.  If he continues to plow the snow across the road, you could try asking the police to speak to him on the grounds that it's a nuisance or a public safety matter.  They may just tell you it's a civil matter and there's nothing they can do, but it's worth a try.