Wouldn't help much in Montana, but do think he would help a ticket in other western states like Colorado.
Montana has only three electoral votes, and three electoral votes would not have made a difference in any election in over 100 years. Not even 2000. (Four would have -- Gore should have gone for New Hampshire in case something went awry in Florida).
Colorado was the tipping-point state (although Pennsylvania was close to being that) in 2012. Pennsylvania probably will be in 2016. Schweitzer likely solidifies Colorado, Nevada, and New Mexico, and could put Arizona in play.