You're welcome. Are you certain there is not an upgrade for the software you want to run? As it is, you'll need to insure that it is compatible with Snow Leopard.
If he's hoping to run PPC versions of anything made by those overly stimulated practitioners of pagan hedonism at Adobe, he'll have to go down that tortuous road I had to travel in purchasing Intel versions on eBay, then go through the nightmare of getting them activated since the original serial numbers will probably not work.
My last pre-Intel Mac OS was 10.4.11. I never tried 10.5.x because everyone I knew said it was a turd, but it was supposed to run older software like Tiger. I ran all my Adobe <hocker*spit*wipe mouth> software under Classic, and luckily for me, I never had any stability problems. In fact, Classic was seemingly more stable than booting into OS 9, at least for my machines.
To the best of my knowledge, you would never be able to install or run even those old Mac OSs with a 2011 Mac anything because of the Intel hardware.
If he wants to run his old software under OS 9 emulation, he can download SheepShaver as long as he doesn't venture any further than Yosemite. After that, SheepShaver won't work. And since SS is no longer being developed or supported, he'll have to settle for that.