There is that "forge ahead and damn the consequences For The Good of Barrayar" aspect to Ezar's horrible war plot that screams Gryffindor to me, but yes, the self-interest part is Slytherin, and whether he cared about Serg's legacy or not, he certainly wasn't self-sacrificing.

And I caught myself thinking that Serg wasn't smart enough to be a Slytherin, but of course that's not really a requirement. However, Gregor certainly didn't get his rational intelligence from that side of the family. (I think Kareen is one of the smarter Gryffindors, or a Slytherin/Gryffindor amalgam, cunning in her self-sacrifice.)