Crackpot.756: That seems to be the main issue here, if we're still talking about the helicopter. It just sits there, teasing you. It may not be necessary to have a helicopter but it's a dick move to put it there and go "lol nope, buy it".
I was miffed about that aspect, too, but then took a second thought. One problem is that it's a multi-player game. If one player in a match has the DLC then every other player needs a version of the software that shows that DLC - at least for something this large and that is not simply cosmetic fluff. In this case, one person might have the helicopter DLC so she jumps in, takes off, and starts flying around air-lifting jeeps and whatnot. If that helicopter didn't exist in every other players' installation then the DLC-renting player would either be flying a green box or doing a Wonder Woman imitation. Which would be cool, but wrong game.
If it didn't appear as a mountable vehicle for those who haven't rented the DLC then that might create a weird case where the helicopter magically appears as soon as someone jumps aboard, or have some players griping about 'cheats' since they can't get in the vehicle.
I'm not sure how to get around those two things. What I would expect to see (and maybe ArmA3 does this?) is that
before the match begins, a window pops up to say "This map contains the following DLC available for purchase. Would you like to rent any of them now, for immediate use?" At least the players would then be made aware beforehand instead of being faced with this "Uh, wait. What? Hold on - what is this DLC and what else does it come with?" mid-game intrusion into the game world.