PPP is polling Alaska this weekend (yes, I know, Alaska polling sucks). They've tweeted about it:
"Dems should not be rooting for Murkowski third party run...Crist like effect pulling more from McAdams than Miller"
So no, he shouldn't be. He could very well end up with 10-15% of the vote in a three-way contest.
The only two rules of Alaska polling that I've found after all these years is the following:
1) It sucks.
2) You have to add a few points to the Republican (at minimum - sometimes it's more) to get to the correct result.