Both my original FS and Wazza didn't do them as a matter of course Luv. They did what's called the "clinical touch" transfer which is transferring "blindly" (though it isn't really because the depth of the endometrial cavity is measured and then an appropriate catheter is chosen to use for transfer).
Anyhoo...I did ask my original FS to do a guided transfer just for sh!ts and giggles so I could see what happens. I had to drink water prior to the transfer and I had the nurse pushing down on my lower abdomen with the ultrasound probe while the FS was watching on the monitor where the catheter was going so he could decide where he was going to deposit the embryo's
When that happens you see a bit of a white bubble on the ultrasound screen so you know they've been released from the catheter (although as you know the catheter gets checked afterwards just to make sure)