Why not just un7zip the file, then recompress it as a .zip?
Also without using attractmode launch the rom with mame and post the output
c:\mame_folder>mame.exe romname -v >romname.txt
I'm going to make assumptions.
Your /romlists/mame.txt does contain
#Name;Title;Emulator;CloneOf;Year;Manufacturer;Category;Players;Rotation;Control;Status;DisplayCount;DisplayType;AltRomname;AltTitle;Extra
umk3r10;Ultimate Mortal Kombat 3 (rev 1.0);mame;umk3;1994;Midway;Fighter / Versus;8P alt / 2P sim;0;joystick (8-way);good;1;raster;umk3;;
umk3r11;Ultimate Mortal Kombat 3 (rev 1.1);mame;umk3;1994;Midway;Fighter / Versus;8P alt / 2P sim;0;joystick (8-way);good;1;raster;umk3;;
umk3;Ultimate Mortal Kombat 3 (rev 1.2);mame;;1994;Midway;Fighter / Versus;8P alt / 2P sim;0;joystick (8-way);good;1;raster;;;
Your umk3.7z file does contain all the .bin files. Double click on umk3.7z to check that. I'm assuming your umk3.7z doesn't have a .zip file located in it.
Your /attracemode/emulators/mame.cfg file contains
romext .zip;.7z;<DIR>
Your mame.ini file has your rom path set.
rompath /mame/roms