Cocoa powder

Is it acceptable to use unsweetened cocoa powder (like Hershey's, for instance) in protein shakes?  I was sleeved 1 week ago today, and my protein shakes just aren't chocolatey enough for me. 

i can't think of a reason why not

I did all the time (and still do,) -  it boosts the chocolate flavor while cutting the sweetness of the mix for a negligible caloric hit.

You might want to consider using Jello sugar free pudding mix.  A tablespoon of that added to a shake was a lifesaver for me.  They have a dark chocolate one that is wunnerful.

I add a half teaspoon Dutch Processed Cocoa to my protein shake every day! It adds to the chocolate flavor and adds a rich flavor that I quite enjoy. Since you are in weight loss mode be sure to measure the amount you use and track it for your daily macros. The carbs do count! 

Definitely ok! My NUT had me add 1 Tablespoon of Trader Joe's cocoa powder to my protein shakes along with 1/2 of a banana just at 2 weeks! It still took me all day to finish 1 - 8oz shake at 2 weeks. But it got easier and it will for you. Good luck!