Can't comment on CrossOver Pro 8 for two reasons - firstly I haven't downloaded it, and secondly it's a beta and hasn't actually been released yet. 😊
I had successfully run the game under CrossOver Games 7.1.1 (running version 1.09 of the game) and also now CrossOver Games 7.2.
The black textures problem is a known and long-standing fault in Wine, and is caused by the game's use of compressed textures. Fortunately you can disable that by running the game with -C.
To do that, choose the "Run Command..." option in the Programs menu, pick the bottle you've installed Emperor in, click "Browse..." and then in the open thingy pick Westwood > Emperor > EMPEROR.EXE and press Open. The Command will then be filled in... Change the end of that command to:
EMPEROR.EXE" -C
At this point you may wish to click "Save Command to Programs Menu".
Click "Run" and the game will run up, and the graphics should work.
What does not work are the videos. Unfortunate that, but they're not essential.