Blocking DHT bootstrap nodes only takes care of DHT. This is only one way of obtaining peers, so even if it's not available, you can still fetch peer information from torrent trackers and receive potential peer addresses from other nodes through Peer Exchange.
DHT is required when your torrent file does not contain any tracker URLs (and you didn't add any yourself). In this case if it's blocked, then you have a problem.
Private trackers typically disable DHT for all torrents (so their torrents don't leak to outside users), along with PEX. It's just a flag in the torrent file, so you can force-enable it if you want (but it won't help much since the vast majority of other peers will probably abide by the rules).
DHT is required when your torrent file does not contain any tracker URLs (and you didn't add any yourself). In this case if it's blocked, then you have a problem.
Private trackers typically disable DHT for all torrents (so their torrents don't leak to outside users), along with PEX. It's just a flag in the torrent file, so you can force-enable it if you want (but it won't help much since the vast majority of other peers will probably abide by the rules).