It would be completely bonkers for an antiemetic to commonly induce an emetic urge in any but rare exceptional cases.
Most seasickness drugs are just first-generation antihistamines sometimes combined with a caffeine analogue to counteract the sleepiness.
Dramamine/Gravol (dimenhydrinate) is just benadryl (diphenhydramine) plus the caffeine analogue theophylline.
Bonine/DramamineII (meclizine) is also a first-generation antihistamine.
Promethazine is also a first-generation antihistamine.
Non-antihistamine antiemetics like ondansetron or scopolamine transdermal patches require a prescription from a doctor and therefore aren't commonly used for motion sickness except for occupational seafarers. And it would still be absolutely stupid if the drugs given to prevent nausea commonly caused nausea.