What you need is something to cache the units so they dont showup til your
within range of them, something like EOS does.
IDK if this could help you but this:
simpleCachev2 for AISSP (AI Spawn Script Pack) SP/MP
A revisited version of the simpleCache script included in AI Spawn Script Pack which does not require to execute any controlled militarize and fillHouse script before.
There is another caching script which i had used in Arma2Co which worked perfect, but Im not sure if it will work in Arma3:
hope that helps.
Welcome to the Armaholic forums btw :)