Can 501c3 participate in a fundraiser if ALL the funds received are going to another 501c3 ( ALL funds received must be in the form of a check, money order or cashiers check made out directly to the receiving 501c3) however, a non 501c3 will be collecting the checks for the purpose of totaling and delivering the funds to the charity.

Sure - one 501c3 can certainly support another. Happens all the time. Some common examples are a church that raises money to support a homeless shelter, or a school that raises money for the Red Cross for earthquake disaster relief.

Thanks for the reply. Someone had questioned the issue because of the non 501c3 collecting the funds for totalling delivery.

One of you contracts with the company collecting funds, even if they aren't charging (and they may want a receipt for a contribution).
If they are charging, one of you pays the bill and deducts it on your taxes. Nor for profits hire for profits all the time.

As long as the checks are made out to the receiving 501c3, I don't see an issue with that. The receiving 501c3 should be providing receipts to all donors.