Tent vs Hammock for Waikaremoana etc

Hey guys, not sure if I should post here or the gear forum so apologies if I got it wrong. I'm looking to start getting kitted out to do Waikaremoana soon and other tramps in the future. Basically I'm trying to decide whether to get a lightweight tent or a Hennessey/similar. A Henessey (with the large hex fly, a self inflating mattress and bubble wind/insulation pads) sound really appealing to me as well as being a bit cheaper and lighter than a good 2 man tent. I've got a good down sleeping bag and thermals which should be warm enough right? On the other hand a tent strikes me as being the more conservative option. Also the DOC site says that camping is only allowed at the designated camp sites, does that mean that I'm going to get hassled by rangers if I string my hammock nearby in the bush? (not trying to dodge camp fees!). It's true that I could just use the huts but I'd prefer to camp out if possible. Anyhow thanks in advance for any advice.