That doesn't seem to work for me. There isn't a filesystem that the disk image can use which will be recognized by both the host macOS computer and Mini vMac. Mac OS 8.1 or later is needed to understand the HFS+ filesystem, but Mini vMac doesn't run OS versions past 7.x. Modern macOS hasn't been able to read a standard HFS volume since Catalina (10.15) and hasn't been able to write to one since Snow Leopard (10.6).
Ah I see what's the difference. I use Tiger to do most of my pre-OS X stuff, it's a bridge between modern systems and old systems. 10.5.8 was the last to write HFS, so yeah I can see that.
Your main issue is that you don't always know what you're dealing with. Is it a Stuffit 1.5.1 archive? 3.0? 4.0? 5.0? 5.5? 6.0?
Mini vMac can only deal with up to about Stuffit 4.0 files. For the others, Mac OS 9 is a good choice. Consider using Sheepshaver to perform "initial processing": decoding and extraction. Since it has, or can, have your main HDD linked, you can simply fire up Sheepshaver and copy from macOS directly, that is, if you're not using an APFS volume, which you could be. If so, then you'll probably want some kind of HFS+ partition somewhere local. Doesn't have to be very big.
Then there's the jump from Sheepshaver to Mini vMac, which is a bit awkward since Mini vMac doesn't really do networking unless you have the LToUDP option, which only works on certain setups. But since you know what you'll be dealing with, you could just drop it into a DropStuff 4.0 archive, then use ImportFI to get it into Mini vMac.
I recommend using something like Creator Changer if you use System 7 on Mini vMac. With Macintosh Drag and Drop installed, you should be able to just drag the .sit file directly on CC 2.8.4, and because you used pre-stored type & creator code profiles, you just pick one, hit OK and it auto-quits.