The words "dehydrogenase", "hydrogenated", and "hydrogenation" are typically (as far as I've noticed) pronounced with "drog" as the most emphasized syllable. That's how I used to pronounce it too. However, when TAing a biochemistry class taught by a rather ancient professor (Ron Brosemer, who has been teaching at WSU since 1963) I noticed that he pronounces these words with the emphasis the syllable "hy". So the "hydrogen" part of the word sounds exactly like it would if it were pronounced on its own.
At first that sounded weird to me, but now I think it actually makes a lot more sense than the typical pronunciation. It may be that Dr. Brosemer pronounces the words that way intentionally for pedagogical purposes. But I suspect that when he learned these words (presumably in the 1950's), his pronunciation was actually the typical way to pronounce them. There is no element pronounced "hydROGen", so it seems unlikely that the chemists who coined these derivative terms would have said it that way in their new terms. I think it is more likely that the modern common pronunciation arose in people (like me) who learned the terms before understanding their chemical significance.
Using Dr. Brosemer's pronunciation with these words, brings to mind their actual chemical meaning, a dehyrogenase is an enzyme that removes hydrogens from one of its substrates, and hydrogenated oils are oils which have had hydrogens added.
I've adopted Dr. Brosemer's pronunciation, and I think you should too.