Dropsy is actually a symptom and not a disease - that is, it is the end stage of organ failure in a fish that has a disease - so there are several disease that could lead to dropsy as the end result - some of them are contagious diease and some are not. Since you know the history of the tank, you can probably make a reasonable decision about whether or not the etiology is a contagious one.
I am sorry to hear that Omnipharous has developed dropsy. I hope he will be happy and pass easily - or maybe even make that rare but not unheard of recovery...

I hope you all will not have to go through this for long.
EDIT:

Roano, I will read all the posts before I start typing since I just saw that I wrote exactly what you did! Good point about the TB.
Has Omnipharous always lived alone?