Some Republicans are helping get Nader on the ballot and/or contributing to his campaign. One such donor is Richard Egan, former Ambassador to Ireland.
These Republicans obviously believe that Nader will be a help to them. Obviously, anything goes in politics, but this strategy projects a "Bush is going to lose" mentality.
The Boston Globe doesn't entertain the possibility that Egan has switched allegiances from Bush to Kerry. I presume they're right about that.