The only way to know is to make a good starter and see if it does anything.
According to the wife (who actually worked in a lab at UPenn with yeast!) you should be ok as long as the container is still sealed and they were keep within a proper temperature range. She said the they jsut might need some more time to get going, but that you should be alright in the end.
Gloucester County Homebrewers
Beer Crafters LHBS (RIP - Store closed 9/09)
1. Slyfox 2008 Dunkelweizen