Would these work with Indy 500 (2 players)
No. The new feature in Stella currently allows assigning each axis only to a paddle - so you get 2 paddles. You cannot assign an axis to a driving control YET (Hopefully the current Dev will keep working on this - read the conversation at the end of the tutorial). In the global settings if you leave "mouse as a controller" set to AUTO, you can use these (or any spinner seen as a mouse by the PC) for one player - just like Stella worked in previous versions.
I would also kill to be able to play 4 player warlords!
with 4 of these (or any CP with 4 working spinners) you could play 4 player Warlords in Mame since it supports multiple mice.