he would have killed them without having a second thought about it.
That may true; because if he was anything like Boba; he was a bad-shebs bounty hunter that didn't care who the target was.
And, I remember that part about "the long game", from O-66 . (I liked that part). And, I like the idea of Jengo planning his revenge; (instead of just taking another job).
But, I still think its possible that Jengo didn't realize, (i.e. he wasn't told) that his army of clones would be working for the Jedi / Republic; and, that it was all an elaborate double-cross.
(I have no idea; but I'm guessing) that when Dooku drafted
Jengo; all he was told that his clones would be enlisted to kill Jedi. (And, if he wasn't told; I think Jengo might've assumed that he would lead/assist his clones in battle against the Jedi).
And it was probably known, (or discoverable) that Sifo Dyas placed the original order; but, Dooku was paying the bills. I think it would make perfect sense to Jengo that the army would belong to Dooku.
Either way, I think I can make myself dizzy thinking of all the possibilities that could have occurred.
The one thing I'm sure of is that Palp's and his Sith-treachery know no limits.