Sorry for the delay in testing.
Tested with the official mame64.exe v.151
It picks up the 7z roms just fine.

It's been a while since I did an install from scratch instead of just replacing files.
There were a couple hiccups. Not sure if it's anything of importance.
First, I got a message from Mala that it failed to create mame.ini
Looking in the folder afterward, there was a mame.ini file present, but I had run MAMEUI once before, so that program may have created it.
I thought maybe mamedev had done away with one of the options for creating the ini, so I tested both via command line.
-cc still works and -createconfig still works.
The only other thing I can think of is that I'm using the 64 bit version of mame which has a different name for the exe.
It's mame64.exe instead of mame.exe, so if Mala is hard coded to use mame.exe instead of the mame executable specified, that could be it.
Or it could have just been a one time quirk.
After that, Mala seemed to hang on "collecting bios", but perhaps I just wasn't patient enough. I gave it a minute, then killed Mala via task manager.
The second time around, everything went smooth. I thought it was hanging on "collecting games", but after 7 minutes the gamelist popped up and Mala was working fine.
Not sure if it's just the massive amount of mechanical, fruit machine, gambling, & non-working stuff that's been added to MAME or if it could still be a Mala issue.
After that everything worked fine.
Log containing first two starts is attached.