I think the Blackfoot look very cool and can't wait to give them a go!
If I were to redesign them to simplify the Counting Coup and change the work boat issue I would do:
Counting Coup: When a blackfoot unit returns to a city with (more experience/more promotions whatever) than when he was last garrisoned you recieve a unique bonus. Cities founded not adjacent to sources of coast gain +2
While not capturing the "significant victory" like the current design, I feel it helps simplify it whilst maintaining the idea. The main reason I like this is it ties the benefit to RETURNING home to Blackfoot lands, so that it doesn't matter how many times a unit has counted coup if he doesn't survive to make it back. It thus reinforces the idea that the tribal leaders are those who are strong and wily enough to win and make it home, and also encourages the Blackfoot to raid and war with their neighbours rather than further flung battles.
It also has a "Victory Parade" aspect to it, after a war marching your experienced units through the city
I added the +2 faith to cities not adjacent to coast as I thought it could be a way to incentivise in-land settling over coastal rather than the "no work boats" restriction, and also mean the Nato-oh Siskoom could be dropped for a UU. I feel like your Buffalo Pound is very unique and fitting and the overall civ design and playability is better if the Counting Coup and Buffalo Pound is combined with a UU rather than another building
Counting Coup benefits I was thinking of were:
XP gain
0-15 Starts a WLTKD in this city
15-30 Culture boost equal to fraction of units strength
30-45 Gains War Chief promotion, increasing strength of adjacent units
45-60 One time tourism boost on all known civs (increased for civs you are at war against)
60- Every 15XP converts to 2-turn Golden Age
Each unit could only achieve these once, but they are cumulative so that if you get 60XP before returning you will activate all of them.
No one unit could farm barbarians for the bonus as you no longer get XP from them beyond 20XP.
I also like how it encourages going honor for at least the "increasing XP from combat trait".
Anyway, this was just your civ design got me thinking, and I can't wait til they're released!