Is it a confounder on not? 
I have a following picture and the assumption that I can estimate the effect of Treatment on Growth by accounting for dT. However, I'm not sure if Unobserved confounder is actually a confounder - it is NOT related directly to Growth. So should I adjust for dT or for nothing?

As Noah points out in a comment, the unobserved confounder is indeed a confounder since it creates a back-door path between treatment and growth. However, the model as presented does not contain a causal path between treatment and growth. Dagitty, which is where I presume your figure is from, will tell you that you can adjust for dT and then treatment and growth are independent: no effect to measure.
If there were an arrow between treatment and growth then yes, the unobserved variable would confound the effect, and it would be enough to control for dT, see attached figure.

