They would appear blue, but then the 405nm would fluorence and then it would result in diffrent color beam and dot, which would be very strange, and BTW a 20mW NUV laser costs way more than a true blue.
I would have to disagree on that... since its just a bluray laser diode that can be purchased for 10s of dollars. Perhaps it'd be a little short of 20 mW (10-15 or so), but otherwise no problem.
On the other hand, i doubt the mixed beam would look convincingly blue, and combining the beams using dichro's and all will be a pain in itself.