Hello SantaT,
I have just purchased a second hand book titled, "Monmouth's Rebels" and I will look to see if your ancestor is mentioned in this.
There must be some records of the trials and sentences as I was given information on an ancestor of mine who was sentenced to deportation to Australia by Judge Jeffreys in Taunton Assizes in 1685. This was, "for his part in the Monmouth rebellion". I suspect the court records are still in existence, these could be in the RO.
I will get back to you but it may be after the weekend.
Jo.