Do you have to germinate seeds before planting them in a hydroponic system?

In most hydroponics systems water either runs continuously or at least daily.
This is much too much water for seeds, so they would most likely rot before they germinate. Therefore you should first germinate the seed in a small pot or small GRODAN plug (around 1.5"). The little GRODAN plug holds enough water, that you do not need to water before the seed has germinated.

Most hydroponic systems have pots/containers that are much bigger than 1.5". For good germination & a healthy baby-plant the 'glove' should fit. Big pots just do not have the best conditions for a small seed. So even if you do not set the system to water, the pots are still too big for a good result.