I've had EBJDs and much of what's been said above is true. Health on them is delicate, it just is. Doesn't matter locally bred or not, acclimated to local water or not, they're genetically delicate and some make it to adulthood, some don't. So Duane is essentially right on that point. Much more of a factor than where it's bred is how robust or weak the particular breeder's strain is. Producing baby EBJDs is one thing, producing a (relatively) robust strain is another.
Almost undoubtedly a healthy Oscar will grow faster than an EBJD, how well they'll get on together will depend mostly on the Oscar, the bigger the tank the better. EBJD, especially smaller ones, do best with easy going tankmates. They stress easily, stop eating, etc.
I found freeze dried mysis to be a good supplemental food for EBJDs, good for growth-- at least that's my experience. I wouldn't go overboard trying to get them veggie foods as long as they're getting a good quality pellet in the first place, not too many starch and grain ingredients. I'd also avoid foods with soy ingredients in them. EBJDs can lose appetite and some develop bloat. Can't personally prove the connection to EBJD, but typical soy ingredients have been shown in studies to cause intestinal inflammation in a number of fish, not what I'd recommend for an already touchy fish like EBJD. Be careful what you feed, some foods, ingredients, or combinations (like soy and peas) are known (in science studies) to cause intestinal problems. You can sometimes kill a delicate fish with kindness, trying to give it "variety" but creating a combination of ingredients with unsuspected consequences.
...Just my experience and suggestions.
