Mac bind to windows domain with wrong name
I thought it could be a machine based GPO that was applied to either the Mac clients or the DNS server.

However, I did a little digging and found this:
http://www.bu.edu/tech/files/2009/10/AD-OD-10.6-1.pdf

Look on page 6.  It specifically mentions about OpenDirectory and how it renames dashes to underscores. It looks like the change is coming from the Mac end of things. Why?    I found this regarding OpenLDAP which is what Open Directory is based on:
OpenLDAP Hyphens within attribute names considered as separate tokens

It appears to be a software bug.