I don't have that book but The Western Rebellion of 1549: an account of the insurrections in Devonshire and Cornwall by Frances James Rose-Troup, starting on page 234 has some information about the various foreign mercenaries.
Sounds like some of them may have been employed to fight Scotland, and were diverted to the rebellion. Others may have already been serving in the English army, but this was the first time they had been used to "suppress an insurrection at home" (top of page 235)
Another book Troubles connected with the prayer book 1549, edited by Nicholas Pocock, has some of the original letters from the Council to Lord Russell, and other documents but I don't think is going to tell you more, particularly as it is all in the English of that time.
Page 62, does mention some of the leaders of the mercenaries identified by Rose-Troup.