I have worked on Wheelman support. Spent a lot of my time (its engine has major modifications targetted to speedup game loading).
Umodel can load Wheelman packages, but I'm even cannot load Texture2D - property format was significantly changes, made it completely incompatible with UE3 properties. I'm fully understand this format, but I cannot integrate in into umodel (and into Unreal Engine too, if its source code whould be available). To support this game I must modify umodel so it's main supported title
will be a Wheelman (all data structures will be absolutely identical
to that game, no variations possible - I'm even cannot reorder fields ...)
So, umodel will not support that game. Only "-list" command is supported. Also, "extract.exe" can extract Wheelman packages.
That's an example when I must spend a huge amount of time and as a result say "it's impossible"