I'm heading up in a few weeks and have been checking here; 
http://www.wta.org/go-hiking/hikes/mount-saint-helens 
for recent conditions  From what I've read, crampons would be overkill, probably the same for snowshoes since there won't likely be any powder to sink into.  I'm expecting I'll go with yaktrax in a few weeks.   
I'd be happy to reconsider if anyone has any firsthand knowledge.