I'm pretty sure the game crashes because your reach one of the limit (for example, RPF archives) not because it have any incompatibility with OpenIV mods.
Problem is, specifically with the MP map, it leads to memory issues like glitched invisible buildings (probably due to the script forcing the game to load two maps at the same time) and crashing if you have any OIV mods like custom cars installed.
I bet it is that. When I merge my add on cars into the Rockstar DLC files, no RPF's are added. My game is completely stable, and I have 100 add on cars, and I am using the MP Map.
So there are a number of ways that the OpenIV team can fix this issue both with the map, and other add on mods.
-Merge it with one of Rockstar's DLC packs.
-Create a DLC pack that can have content added to it. It has a limited amount of RPF's. So if you wanna install a map or a car, you run the tool and it adds the data to the equivalent files. Where ever possible, don't actually use RPF's. Just use folders. I am not sure if it is possible to simply not use RPF's inside the RPF, but find a way to cut it down. If you can't have the files in folders, maybe have folders in their RPF's. For example, in the RPF for vehicles, have folders for the vehicle files, and mod kit files. But if you can't do that, maybe come up with a prefix naming scheme. So for example, with LC, have the prefix be the name of the folder it was in for GTA IV. So all of the files in manhat01 would have file names that start with manhat01_[name].ydr, manhat01_[name].ytd, manhat01_[name].ydd, manhat01_[name].ymap, manhat01_[name].ytyp, etc...
-Crack the RPF limit to allow more RPF's. I should point out that in the next update for GTA Online, Rockstar may have to do this, especially if it is a large DLC. It is ether that or have the files organized in a way that minimizes the number of RPF's.