Since Colt's "commander" hammer did not come out until around 1960, I think any intention of use by cavalry would have been a bit late. Other pistols, e.g., the Radom, had that kind of hammer earlier supposedly so it could be cocked by rubbing the gun across the saddle. (The Poles found to their dismay that while they were worrying about horse cavalry cocking their pistols, the Germans were building tanks.)
Actually, the rounded top hammer was used by Browning early on and the very first .45 model, the 1905, had that type hammer; the U.S. military decided on the spur hammer so it could be more easily cocked when the pistol was held in one hand (the other being needed to control the horse).
Jim