I was wondering if you can play with a mod in the regular Soldat server?
It is because i have never seen anyone with modded guns or the sort.

Yes.
Mods only change graphics and sounds. Even if you have a modded gun the others will only see the gun that their mod (or the standard install) shows.
There are mods though that change the animations of the game. You cannot play online with the modded animations, but most mods are playable online.

Thank you for that clear up