So recently i found someone that submitting his game to every jam possible. But but the thing is, he only submit his game to jam that didn't have a strict rules on theme. so when there's word like "There is no strict theme" or "Choosing a theme is not mandatory if you already have an idea. Keep in mind that games that make use of at least one theme will be judged more generously than those without." in the jam rules this guy would submit his game. and i think this quote from this guy really summary what he is doing

If you’re looking to promote your game, look for jams that have some relation to your topic and the most submitted. Hot tip from me.

So yeah, is this allowed ?

im not native english speaker so sorry if what im saying is a bit confusing xd

Submitting a game to lots of jams for attention is frowned upon here. Even if you technically don't break any jam's rules, it's still not nice and will be considered spam. So please don't do that. Jam organizers talk to one another, and people caught spamming are often banned from all future jams.

If in doubt, ask before submitting. Most jams have a community for things like that. And keep in mind that theme isn't the only way to decide if your game fits.