Snapedom

I may be recalling this incorrectly, but wasn't Cresswell (the only muggleborn with a career we know of) one of Sluggy's? That blood status didn't come into it with him is rather the point - whatever the views of blood status with Dumbledore's circle and Gryffindor house, the general view in society seems to be rather more muted in truly accepting muggleborns (even if it's not openly said by everyone that they are thought inferior). Plus, since the WW seems to run on an old-boys' network system, muggleborns are disadvantaged from the start by a lack of connections. And the Gryffindors are not depicted as being particularly good networkers; it's very individualistic there with at best small groups of friends. Having a well-connected patron who DOES NOT CARE about blood is the muggleborns' best shot - with Sluggy they actually have a chance at establishing the connections they need.

It's not that he FAVORS them, it's that he offered them a real, stable link with key sectors of wizarding society they would not have otherwise had.