A survey will most likely consist of a review of the paperwork for the airframe, engines and avionics, and an inspection of same (against the records) by a LAME who is experienced on type.
So for a HT2 or 3 you want a guy (or gal) with experience on the Gazelle who can advise you about what is right and wrong with what is written down in logs; what is due for replacement on time and what is not looking so good based on experience.
You will probably pay for a day's
services so plan the day out and have a list of questions to ask about the airframe, head, blades, engine, avionics, etc. Many ex mil machines have been maintained to a very high level. The question will be whether certain parts have limited time and what the replacement cost will be for those parts.
... ex-military gazelle that seems ideal for my personal use ...
Probably not if you are a low hours pilot. Check out the accident stats for ex mil Gazelles and low hour pilots. Also the costs of parts. With a permit aircraft, you are very restricted on (legal) usage.