There would be some issues with enemy location setting (used to find PC party members if they stealth or go invisible) and dealing with creatures on the other sides of doors. There could be some other minor issues from the quick look I did. Most of the AI is in a script called script hench_o0_ai so most functionality would be OK. I also think that compiling the script with the latest version of the AI would work fine with the older version that is part of the base install.
I would suggest looking at overriding the hench_o0_initialize script instead. This script is already run once by the AI for enemy monsters at the start of combat. It creates items and does some prebuffs of monsters if the AI global options are set. It does not have the PC object, but that can be obtained by calling GetNearestCreature(CREATURE_TYPE_PLAYER_CHAR, PLAYER_CHAR_IS_CONTROLLED, OBJECT_SELF, 1, CREATURE_TYPE_IS_ALIVE, CREATURE_ALIVE_BOTH) - maybe different parameters if you want the PC only. There are some rare monsters that can run the AI without a PC present, in that case call DeleteLocalInt(OBJECT_SELF, “HenchAutoIdentify”) in the script to rerun it until you get a PC. Just make sure the original code in the script is only run only once. If you override hench_o0_initialize, use the latest scripts from the 2.4 AI, it has some bugfixes and will work with no issues in the base AI.