I'm sorry for your loss; losing a spouse is very difficult. And welcome to FlyerTalk!
IMO, there could be other repercussions from using his account for your award travel; I suspect there might be a much "cleaner" way to do this:
If your spouse had a will or testamentary document with you as beneficiary, you can have his miles transferred to your account.
See:
http://www.flyertalk.com/forum/ameri...solidated.html