They won’t respond to an inquiry like that, and they definitely will never give a solid “yes” or “no” answers. What a program is capable of later could vastly change from what it currently does.
I wouldn’t risk using Reshade on my account. But you do you.
Edit: there’s also so many variants of Reshade that there would be no way to give a broad approval or not. And with so many variants, it’s likely at least a few run foul of blizzards rules. While sure you may just like the look of other players being neon blue, having neon blue players running around in a PVP match would be an unfair advantage.
Edit 2:
Its old so please do not post there! But the below statement from a Support Forum Agent is likely the most official reply you will get.