How would trick-or-treat for UNICEF be much different from the bell ringers for the Salvation Army in regards to panhandling? Sometimes, you've just got to ask, and if it involves the particular holiday spirit, all the more props to them. :)

And the orange boxes would go well with an orange Dalek...

I would think a college student asking for money would be more justified than one asking for candy. I've had a prof ask me "Aren't you a little old to be trick or treating?" but you're never too old to help out a charity!