I think the chance is high. Question is, is it a local serial killer? Or someone who travels to Idaho, for whatever reason?
I read many times that SK "hunt" not so far from home. Israel Keys seems to be an outlier, but maybe not. It is quite possible that he simply moved frequently due to work, and his kills were not that far from periodic abodes.
So a serial killer who ends up in a student town, who could he be? Either he belongs to a student group, or maybe is from the teachers cluster (why not?), or he has a hobby that frequently brings him to Idaho?
We said, hunting. I would think, skiing, including cross-country. There are star garnets in Idaho, maybe someone mining stones in US/Canada? This corner, Mo-ID-Ore-WA-BC is the prospectors' haven (In this case, the connection with Oregon is possible - Oregon sunstone and agate, need to check if that area is far from the Oregon murders).
Another question, we have always looked at ID or WA when we discussed crossing Canadian border. What about traveling to the other side, Montana or North Dakota, and crossing there? Or in general, could the killer be from Montana? I understand that statistically, Montana is not as populated, but it is possible, as it is very close to Idaho.
P.S. I looked up the mining places. Between Fernsdale, ID and Moscow it is about one hour. Sapphire Mountains of Montana are on its Western side, close to ID border. Oregon sunstones are not that close to Salem, in its East-Southern corner, but not that far from Moscow. Just an idea about another job that might bring a traveling SK to Idaho.