Can you bring them in from outside? Good question. I suppose you could, if you were 100% positive that you were collecting from an area that has NEVER had chemical fertilizers introduced. If you even have a. 0000001% of doubt. Don't use them. Chemical ferts were all the rage back in the 60's and 70's in the U.S., not sure about Canada. I just order them online. I don't like having doubts.
Yes, they are 100% safe for your frogs. Not i, nor anyone else on the forum would ever recommend something that would be unsafe for your frogs