My team was standing close to an enemy that was standing in the open. So I decided to throw a knife on his head, and the first knife misses completely. That was odd I think because it's a high dex merc only 13 squares away, so I run forward with another thrower. Miss. Ok try again, this time on torso. Miss. What the... okay, I have 6 mercs that can throw at least one knife within 15 squares. I now try hit his torso. All misses. So I have 8 knives, where 6 of them completely misses the target.

Mercs: Sidney, Raven, Blood, Wolf, Maddog, custom merc (85 dex, 80 str),

There were no obstacles. Well, you can judge for yourself from the attached picture.

The attached image is from a round after the attempt. The merc threw a light break and fired off a shot.

This happens very frequently when there is grass around, so I guess don't use throwing knives when there is high grass/hay nearby.

I've also been in the situation where a merc is 2 squares away from a target, does 2 burst fires on torso and misses everything.

Is there some mod out there that can check whether the merc has a chance to hit without completely altering the game? I was watching some JA2 1.13 videos the other day, and it had a bar that showed the percent chance to hit, which I liked. So is there a way to just grab that?

As far as I know, there isn't any such mod, but why not use 1.13? As I've said before, anything you don't like in 1.13 you can turn off, feel free to ask me if you need any help.
As for the problem, it might be that the JSD (more or less the structure of an object) is messed up, and while it is possible to modify it, it is a bit of a mess to do so (grab an SLF extractor to extract the necessary files, then a JSD Editor to modify the proper jsd, then add the modified jsd back to the slf).
So, easier way would be to just grab 1.13

I guess it's my only option then, so I installed it.

I like the upgrade so far, the seems more realistic and has tons of options. Thanks.