Let's put it this way, a lot of companies are very happy when I use their gear. For the simple reason that they can sell their gear, as I said before it's a win win situation. Often with workshops I'm also having the guys from the gear in the group so they can help out students with specific questions and let them try out gear, we recently did a larger workshop with a Medium format reseller who brought 5-6 bodies with which the students were allowed to shoot (on their own card).
I think it's more :
Artist : can I please hang my work here because I can sell it.
Gallery : but of course you can hang your work here because we get a nice commission when we sell it.
Also do realize that many, many workshops are sponsored, this varies from door prices to gear.
Elinchrom makes sure that I get my gear in most countries, I promote Elinchrom.
Companies like NIK, OnOne, Expoimaging, Tethertools etc. give doorprices or small prices for raffles on the bigger workshops and they are certainly not doing it for free
When I promoted Expoimaging on the recent Professional Imaging one hour after the show there was no flash bender available anymore on the expo floor
As mentioned before it's a win-win situations for both parties. And they go really nice together.
Do remember however I'm not a "starting" workshop teacher :-)