I'd second what Sylvia says here... the Interpet "internal bacteria" potion even has a dwarf gourami on the box!
Everything I've read and heard suggests that the bacteria is endemic to commercially bred dwarf bacteria, i.e., they'll be carrying the bacteria whether you quarantine them or not. The question is whether or not it becomes a problem. The sad fact is that in many (perhaps most) home aquaria, dwarf gouramis only last six months to a year, if that, whereas they should live for at least 4 years (their maximum lifespan in the wild).
Hard alkaline water, nitrates above 40 mg/l, any trace of nitrite, and low temperatures (less than 24 C) are all quick ways to stress your dwarf gourami and make it more susceptible to disease.
Personally, whenever friends of mine want to buy these fish, I recommend against them. They're nice fish, sure, but unless you can provide exactly the right conditions for them, there are hardier alternatives to look at. Honey gouramis are definitely nice fish, and there are also some very nice small African climbing perch. They can be a little shy at times, but they're full of character. Ctenopoma fasciolatum is a lovely species, for example.
Cheers,
Neale
One last thing of note is that dwarf gouramies are often prone to disease - especialy highly contagious internal bacterial infections such as those which cause dropsy. They can carry these things into your tank and introduce them to your healthy fish. One way to avoid the spread of disease is to provide the fish with excellent water quality and as stress-free an environment as possible. However, the most certain method of prevention is to quarantine your new gouramies for a month or 2 before adding them to the main tank.