I can't tell you much specific about Riverton, haven't lived there but did live in Thermopolis which is about an hour away. It is not Indian Reservation itself but is on the res and surrounded by reservation land. There is also an 'honor farm' there. It's not a pretty place at all. I would not want to raise my kids there, but again, I haven't lived there so take it with a grain of salt.
As for homeschooling, Wyoming is pretty easy. You just have to submit your curriculum covering the 7 core subjects (I don't remember what they are) each year. The state cannot approve or deny your curriculum, it's just records of what you are using. Documentation is only required between the ages of 7 and 16. Look up Homeschoolers of Wyoming (H.O.W.)
For Midwifery, it just became legal in Wyoming a year or two ago I believe. I don't know how many midwives, or where they are. Riverton isn't too far away from Lander and there may be midwives there. It's a much more 'crunchy' type place than Riverton. Riverton is the complete opposite of cruncy.
Hope this helps some and sorry I don't have more specific info.