Can't see why not, It's a risk vs reward thing. You'll probably be getting turned into some fine red mist every time though.
Actually what you should do is make it a buyable upgrade for vehicles. It grants units to latch on at the risk of being shot on the outside.
mmm no there is no Defiler with Transport capacity, i can you link you the page of codex Chaos Space Marine
Hmm, I used to play Unreal Tournament 2004 and riding vehicles which didn't have passenger seats/full by standing on them was a great way to get around! Once your in combat it generally makes sense to jump off
You are right actually! As the lore would have it, Khorne Berzerkers do sometimes attach themselves to the Defiler to get a ride into battle. Now, I don't know if the Defiler will be in the game, but we do have a legit example.