Okay... Those settings don't work. Reason being... the vein displacement eats the hair displacement, if the hair displacement is lower than the vein / musculature etc. (You know, the ole M4 displacement maps) So it'll have to displace above the vein map. And... ugh. Seriously ugh. He looks like someone threw acid on him lol.

So the Math:add isn't going to work. At least not this way.

Settings for my acid victim are what you suggested, but with the hair disp increased to .4 to see if I can get the hair above the m4 displacement.

Ergo:
Displacement parameter = 1.0
Math:add = 0.4 for both materials

Result....

Silke