I don't think its a problem at all. If people want to listen to the feed then it's a possibility that they will donate. I have some very dedicated listeners that rely on my feed to get weather info or to see if little Johnny is getting arrested on the local warrants.
Sending you 10-15 bucks is still cheaper than buying a digital scanner. Plus, they are still getting the option of listening on phone apps and such. This has been mentioned before on the forum. There is usually a mixed bag of comments about it.