Generally, progressive jackpots are paid out by the network that supports them, unlike local slots winnings that are paid out by the casino. If you are playing a progressive slot, and you have some small wins without hitting the main jackpot, those wins are paid out by the casino.
If you are playing with progressive free spins, the wagering requirements are usually applied to those smaller winnings. Because the network pays out the main progressive jackpots, if you win the massive main pot, the wagering requirements will not apply. Imagine having a wagering requirement of 50x the winnings on a massive $1 million jackpot? It's completely unrealistic. However, all casinos have different terms and conditions, so please read these thoroughly to make sure you understand how the wagering requirements apply to any winnings.