Are there any known Jedi or Sith from the Ewok species?
It seems to me that any species with enough intelligence is capable of becoming Force sensitive.
For what it's worth, according to the first Star Wars D20 RPG book, there is a distinction between "Force Sensitive" and "Jedi" where Force Sensitive is the ability to use the force and Jedi/Sith is how it was used.
Ewoks in the D20 book were able to become Force Sensitive, but as of Return of the Jedi, no Ewok had been. It is implied that a Force Sensitive Ewok would likely be a Shaman. The striped Ewok with the skull on his head, named Logray in the Legends continuity, actually was Force Sensitive in the Legends continuity.