Is tank vent hose necessary?
 

Just ripped the CA Vapor Can off the bike, and Im wondering if I have to keep the tank vent hose running down the frame and to the ground, or if I can just have the tank vent to atmosphere?

05 883l carb rubbermount

If you over fill it, it goes in that hose and runs out on the ground. At least mine does. I did over fill it once.

If you just run the vent hose (no can) you are venting to atmosphere. I would keep it, in the event of the tank being full to the brim (yah it happens, lets be honest here) the vent will probably weep a bit. Or while riding you may splash some up onto your vent and it may weep. With no hose it will weep onto the top of the frame and the wiring that runs down your top tube and also probably onto the top of the motor.

Ever seen like a small filter or something you can stick on there?

Yes keep the vent line as you probably don't have a vented gas cap on a CA bike, there are small filters that look like tiny K&N's that people use for crankcase vent lines, you could use one of those if you want, here are some images.
https://www.google.ca/search?q=crank...w=1680&bih=919

I like the idea of that filter. Could I just attached that pretty much straight to the tank vent ( small hosing would be required im sure ), and have it hanging there by the tank? that could look kind of badass!

Sure...badass....or kind of silly. ;)

Haha fair enough!

Personally I would run a nice looking hose like a braided stainless hose down to the bottom of the bike and if you want a filter put it at the end, that way if there is any gas overflow thru the vent line it will drip on the ground instead of all over your leg.
The filter really isn't necessary and will serve no usefull purpose on a tank vent.

Love the idea of the stainless braided!