is Doubanjiang (sezhuan hot bean paste) an acceptable substitute in recipes calling for gochujang (Korean hot sauce)?
Both are mildly spicy, but the similarities end there. Gochujang is tangy and slightly sweet, whereas doubanjiang is more salty, savory and fermented-tasting. Even the textures don't match up: gochujang is smooth, while doubanjiang is chunky and ragged. I wouldn't substitute either one for the other. 

Incidentally, if your doubanjiang is just sitting there because you got it for some elaborate Sichuan recipe involving like eight other seasonings... doubanjiang is more flexible than that, and will work well as an addition or even just on its own. Try frying up some ground pork with a bit of doubanjiang and some scallions, served over rice.