By man-made varieties, they just mean the specimens that are tank bred and have been selectively bred over generations for their bright colors. They are usually the commonly available ones, because the ones selectively bred ones sell better because of the appearance. The red variant, for example, is not natural but has been been bred for.
The virus they are referring to is called dwarf gourami disease. It is a virus that has been blamed for quite a few deaths in the last decade and has been said to have contracted by fish from large scale breeding operations, particularly those outside of the US. Now, viruses cannot be readily identified without a lab and microscope in a lot of cases, so there is debate about how much has actually this virus versus just an overall a decline in the commercially bred population quality. I will leave that research up to you, but I will say that I usually suggest an alternative like the honey gourami instead of the dg when it is available.
As for how hardy they are, that depends on the fish and the circumstances. I see A LOT of troubles revolving around them, so I personally do not believe they are the hardiest of fish, they can tolerate a higher temperature range than some other fish, but I wouldn't say that is indicative of their overall health. If you want to try one, they are gorgeous little fish and just look for a healthy looking one from a good place. Plenty of people have kept them and really enjoyed them. If you would like to consider an alternative, consider the honey gourami or the thick lipped gourami or the paradise gourami. Up to you though. As long as you find healthy stock from a good place, you will probably be fine. I hope that answers your question a bit, if there is more you would like to know, feel free to ask.