Can I use this HUD? (CS:GO)

No.... its only a reskinning of the HUD like for example you dont get banned if you install a weapon skin... you should be just fine with that.

You can't be banned for using custom HUD. TF2, for example, has alot of custom HUDs, in additional Valve made special folder for custom content...

I think they disabled custom HUDs because of some bug, not 100% sure though.

Pretty sure it's okay.

No. You can't use anything custom in Match Making. IDK about casual but I'm pretty sure you can't there either because I can't delete background.swf anymore to fix the CSGO memory issue. It'll say you have modified your game files and you need to verify your game.

Real players don`t use any HUDs. we just feeeeeel the game.

it says right in the top of the op page link :

Valve has temporarily disabled custom HUDs in CSGO. Stay tuned for more information soon.

how current that is I cant tell ya - im way to casual a cs:go player to do anything competitively.