Bullshit, Trackers and DHT hold IP and port of peers, hole-punching technique allows to open both sides.

The only difference is the speed to establish connection:

• With an open port, it is done instantly as peers can reach you directly.
• Without, you need to wait for the seeder to fetch your IP from tracker (slow) or to recieve it from DHT (fast).

Now, the reason why it seems hard to seed torrents on private tracker, that disable DHT, is because seeders with closed port will only fetch leechers IP from tacker 1 to 4 times per hour, so by the time the hole-punched connection is established, leecher has already sucked up all the data from peers with open ports.

It’s fine to keep port closed if you avoid private tracker and DHT disabled torrents. If you want to build up ratio on a crappy private tracker, seeding a piece of a fat 100Gb+ torrent will do.