I'm no pro on the scripting front by any stretch of the imagination so I may not have all the knowledge about this. If I go wrong someone in the know will hopefully point out any mistakes.
I think you need a different ACM for each group or unit but not 100% sure. Never tested it yet.
At any rate this is how you can control an ACM you place and the control options that I know of so far.
I place an ACM module and name it BIS_ACM. Then I create an init.sqf in the mission folder with the following code..
// Waits till the Module has activated.
waitUntil {!isNil {BIS_ACM getVariable "initDone"}};
waitUntil {BIS_ACM getVariable "initDone"};
// All spawned units will receive an ammunition package (Ammo ammount) based on a
// randomly selected value from this range. 0=minimum 1=maximum
[0.2, 0.5, BIS_ACM] call BIS_ACM_setAmmoFunc;
// Sets the factions that will be spawned by the ACM.
// Options are USMC, CDF, RU, INS, GUE
[["USMC", "RU"], BIS_ACM] call BIS_ACM_setFactionsFunc;
// Intensity controls how many patrols may be active at a given time and
// how often patrols are spawned. 0=minimum 1=maximum
[1, BIS_ACM] call BIS_ACM_setIntensityFunc;
// All spawned units will receive a skill rating randomly selected from this range
// 0=minimum 1=maximum
[0, 0.5, BIS_ACM] call BIS_ACM_setSkillFunc;
// set specific minimum and maximum spawning distances for ambient patrols.
[BIS_ACM, 300, 600] call BIS_ACM_setSpawnDistanceFunc;
// This function can help to define a custom pool of patrol types and associated chances.
// 0=minimum 1=maximum
// A value of -1 will remove that type from the pool.
["ground_patrol", 1, BIS_ACM] call BIS_ACM_setTypeChanceFunc;
["air_patrol", 0, BIS_ACM] call BIS_ACM_setTypeChanceFunc;
See the comments in the code to get an idea of what everything does.
The units that spawn are randomly generated from the group options you see in the editor. Apparently some groups appear rarer than others but I have no idea at this stage if the mission creater (i.e. us) can actually define what groups appear and what groups don't. The only option close to this I know of is at the bottom of the code I posted and that just defines air or ground units in general. You could end up with loads of armor running around blowing the place to hell or infantry swarming all over the place or a mixture of both. It's all very random but there is some control.
BE AWARE if you attach an ACM to an AI and that AI dies the ACM is gone and will no longer generate units. Also any units it had generated will most likely leave the area and dissapear. Not sure if this applies to respawning A.I. (Again I aint tested that)
Hope this all helps.
P.S. Always remember if you make changes to the init.sqf you need to reload your mission for it to take effect.