Is it myth or possible and if so should you try.

It is quite possible to Vibrato on horn. It's just not very popular in America, don't ask me why. But I do it from time to time. Just don't overdo it. It can sound annoying.

I was bored one day and figured out vibrato on horn. I found some good web resources, and decided to go with the wiggle-fingers-in-bell method. I personally thought that it sounded really good on lower notes, but not very much or very frequently.
Brad

When I was i high school, I figured out how to do it by wobbling my throat muscles, much the same way I do when I sing. My band director gave me a big frown when I tried it at band practice. Haven't tried it since! I've heard recordings of European horn players playing with a such a heavy vibrato that they sound like saxophone players. It's really gross & annoying. Who wants to sound like a sax player? BUT, I've heard a few horn players do a very light & mild vibrato that sounds beautiful. Michelle Perry of Empire Brass uses light vibrato in certain pieces & sounds lovely. Dennis Brain used ever so slight vibrato one certain notes when he played the slower movements of Mozart's horn concertos. It's all a matter of tasteful application. To much is sickening, but just a little here & there in solo work can be lovely.

it's definitely possible i do it all the time in jazz band at school to mess with the director and our music

It really helps if you get into the music too, a few parts where in the phrasing it goes well... Even though it might not be smart to stick it everywheres in case you're not really supposed to be doing that at all.

Vibrato is possible on the horn (as everyone else has said!)
It can sound quite nice when not over used. It gives some shape on notes. Its quite popular in Europe.

I figured out how to vibrato on trombone, and then tranferred that same technique over to French horn. I can do it, but I have never used it during a piece of music. I think it sounds better with a solid, straight tone.