Yes. Would you rather have a Democrat in there? The seat would be locked down to "D" for the next 18 years at least, giving no hope of someone more conservative in the seat. Remember which seat it is. It has a very liberal constituency, a conservative could not have won, not a chance. But with a Republican in the seat, someone slightly more conservative could challenge him in a later primary and win. Think long term.
Brown IS a Democrat, he just has an "R" after his name, Spectre was the same way.