The hats opinion's is about personality traits, and as he is one of the biggest pushers for house unity I doubt he would support Salazar's opinions. Also I looked it up to se if it really is unreasonable:

-[quote]During a webchat in 2007, J.K. Rowling mentioned, in a response to a question about Slytherin house, "Slytherin has become diluted. It is no longer the pureblood bastion it once was."

The comment was made re: a post-Deathly Hallows Hogwarts and Slytherin, which is to say that by the time Harry Potter's son, Albus, was heading off to Hogwarts, blood purity wasn't a significant defining factor of Slytherin.[/quote] Seeing as we're halfway there I would say that muggleborns must have been trickling in, maybe not fully accepted but it would be a thing in progress.

-[quote]"The proportion of the wizarding population that is Muggle-born is on the rise as the pure-blood families shrink in size and number."[/quote] if they kept up with only purebloods and halfs then Slytherin would cease to exist as a house.

Edit: reading on found thi[quote]Personality traits of students seems to be the main factors the Sorting Hat would use in deciding which house students were placed in to; ambition, cunning, cleverness all seemed to be among the most important qualities in determining which students ended up in Slytherin, more than blood-purity. [/quote]

edit2: and this [quote]Finally, in Chapter 23 of Deathly Hallows, Scabior (the Snatcher) suggests there have indeed been muggle-born members of Slytherin, though not many.[/quote] I should look that up.

Anyway, personality wise I just think that's were he would go. 

Another edit: if things were still touchy maybe the hat would recommend him another house, probably Ravenclaw, so if it's really bothersome I guess he could go there.