here is is how it works. (Probably)
First you have to create a requester module in the editor and set it up as usual. (Synching requesters and providers etc.). Call this module "myRequester1" (no quotations) and set the support limit to 0.
To add unlimited Artillery Support - at some point of your mission - you would first (eg.) create a trigger with a condition (eg. !alive hunter1).
Then into your trigger on Activation field add.:
[myRequester1, "Artillery", -1] call BIS_fnc_limitSupport;
In theory, once hunter1 gets destroyed you should be able to call in artillery support for an unlimited amount if times.
Unfortinatly I have no access to ArmA right now, so this is untested but if it fails I'll check it out tomorrow.