This is one of those cars i cringe of when someone asks security light issues lol
Here's some things to look at.
1- did the client have the ignition barrel recall done? If so, this may change the type of passlock system the car would have. I've seen this on a chevy cobalt before and had to use a passlock-sl2 for the passlock bypass. May not be related but thtought i should bring this to light,
2- Instead of grounding the evo through datalink, ground it to pin 4 or 5 at the OBD-II. Two ground wires exist there, bcm ground and body ground. Try both, i forget which pin is bcm ground but you may need to ground the unit there and also the remote starter.
3- If problem is persistent even with the key, the passkey fuse may actually be blown. Try starting withoug the evo or remote start connected at all to see if problem persists.
4- Do you have black tape to cover the light? :P (kidding)