Could you add an event that checks player if he is vanished?
I just want to recompile TeleParticles plugin to allow players in vanish to autodisable effects.

Do you want to listen to an event which gets called when someone's vanish status changes, or do you want to be able to check whether someone is vanished at a particular time? Both are possible as far as I know.

In my situation will be best second variant. It would be nice.
For example, I want to add event to TeleParticles that checks if player wrote command /v or /vanish and check Essentials vanish status. If essentials returns true or false, teleport effects and sounds will be enabled or disabled.

You can listen to VanishStatusChangedEvent which will fire whenever the player is vanished or unvanished.