I've never heard that. One guide I use about the act of using cuttings simply says to use the hormone. It doesn't say "exception"....so I assume unless the guide for the particular plant declares you shouldn't, I figure any and all can use it.

As with any cutting, you should take a number of them....at least a half-dozen..just in case.
So, if you like, why not try a couple without the hormone and a couple with....and hold a couple in reserve. See what happens.

Should you be using vermiculite as your geranium cuttings medium, no rooting hormone is necessary.

Geraniums will root in virtually any moist medium. Hormone isn't harmful, just not necessary. During the winter here, I have been known to simply take a piece of an interesting variety and put it in the ground where I wish it to grow. The same works in pots.

Ryan

I have spoken to commercial pelargonium growers, none of whom use rooting hormone for cuttings. One grower uses a solution of Vitamin C powder* as a rooting aid, others nothing at all. With one exception (Mabel Grey) I have had no problems with Pellie cuttings. One other point do NOT close up or tent pellie cutting as they will rot. Keep the compost warm and the cuttings in a light warm place and they will root in a few weeks.
* Vitamin C solution: 1/2 teaspoon vitamin C powder in 50ml cooled boiled water, store the solution in a brown bottle. I make my solution up fresh before each cuttings session.
PS Do not use composted bark for the cutting or planting media as it retains too much moisture.

I have heard that you shouldn't use rooting hormone on anything edible. Maybe they are considering that some people might use the scenteds for culinary use.