Do people use soap on their tall boots at all? I only use mine for showing so they don't really get that dirty, just dusty - I wipe them down with a damp rag, then polish them. But if they got really mucky, would some saddle soap wreck the finish on them? Obviously you'd have to polish after.... Just one of those things I'm too chicken to try on my own boots
Scrub off the muck GENTLY with a soft nailbrush under running water, and pat dry.
While they finish drying, google "spit and polish" or similar on how to condition your boots and get them really shiny.
If you want shiny boots, follow the instructions and only use proper boot polish, not anything meant for cleaning tack. But if they don't need to be super-shiny, go ahead and use tack cleaning stuff. They won't be shiny, but they will be well-conditioned.
If you polish them up properly, the layers of polish protects the leather and makes them much easier to maintain.