I found some downloads for Mac versions of Lemmings and ONML, unfortunately, they are compressed archives in the .SIT format. StuffIt expander should be able to decompress them, but the one that comes with the Executor Mac emulator couldn't seem to do anything with them.
So I'm stuck with the demo ONML for now (thank god they have that at least!)
But even with just the demo, I have verified that many of the tricks/glitches that works on the PC and Amiga also works on the Mac. I have verified in particular:
1) The Fun 6 glitch (
screenshot)
2) The Tame 20 glitch (
screenshot)
3) The miner glitch (used for example in Havoc 10 17/21,
screenshot)
4) The Mayhem 10 glitch (
screenshot)
5) The Wild 15 glitch (screenshot purposely withheld)
6) The glitch I used for the 1-builder 77/80 challenge to Mayhem 17 (screenshot purposely withheld)
I haven't verified more because I'm too impatient to solve the levels and don't have the access codes to go to any particular one in the demo.
Overall, I'd guess that many of the challenges that work for PC will have a good chance of working on the Mac also.