Wow they are great!
You can embroider on anything that holds a stitch. The problem with embroidering on leather of the weight for a handbag is that it is very heavy and you would need specialist equipment to do so. You may find that they are painted or appliqued.
That said, softer leather, like that used in gloves, is fun to embroider on and, especially in Elizabethan times, was very common. There are some beautiful existant examples of leather gauntlets that were embroidered on the cuffs. I have some soft leather here at home that I intend to make into a pair of Elizabethan gauntlets sometime (complete with very intricate cuff embroidery).
That's the best thing about embroidery - it's all about experimentation and seeing what works and what doesn't.
