Has anyone tried, or think would work, using Only War to make a Traitor Guard regiment and running a game from their point of view?

I see nothing at all stopping this.

As long as the traitor guard are dealt with as humans who are rebelling, rather than full on chaos worshippers, then there is nothing you'd need to change within the rules.

Maybe once you reach certain levels of corruption you could start offering some of the mutations and gifts from Black Crusade?