The ones that he/she owns.

Is it safe to say that a Hammond A100 or B3, Fender Rhodes and some Vintage Fender Reverb amps would be most desired in a studio by these people?

Sorry. Who are "these people?" What is your market? Is this some "let's start a studio" (literal) pipe dream. Or are you trying to sell services to specific people. Most people have no idea how to turn a Hammond organ on. Don't know how to work the "on" switch. "Those people" don't "expect" a Hammond. No one "expects" a vintage tube amp in a studio any more than the expect the Spanish inquisition. Most gear in working studios is owned out of self defense. To protect yourself from stuff that goes hummm, snap, crackle, and pop after being out the on the road. Yes, good gear can be a selling point. But I'll be shocked if someone pops in to say that, "you can't call yourself a real studio unless you have a pre-CBS tele, strat, p-bass, Bassman, Deluxe, and of course a Harvard."

I'm sorry, but the phrase "[[url=http://[/URL]="http://www.youtube…"]Is it safe[/]="http://www.youtube…"]Is it safe[/]?" brings back memories of a time in a drive in movie theater when a certain young lady was desperately looking for things to do other than watch the movie.

That is true, you bring up great points Bob... I was just curious since many small studios that I have been looking at recording with have a few of these vintage instruments here or there and I was seeing if there was some unspoken standard or expectation for this stuff among other artists.

Studios used to be expected to have a piano and maybe a Hammond. Today, a studio with cool backline gear can better attract a certain kind of client, and better record the folks who come in with the cheapest junk they could find in a catalog. There's no standard expectation, but a Rhodes, a Wurlitzer, some analog synths, 40's - 50's guitar amps (off brands too), are useful and sex the place up. I personally don't feel that a huge investment in vintage guitars is warranted, but some well-intonated guitars and basses that do not hum can also be session savers.