Vivitar doesn't make its own cameras. Instead, it rebrands models from 2nd and 3rd tier manufacturers. Usually these manufacturers are based in Taiwan, mainland China, etc. And these cameras aren't often submitted for reviews, so it's hard to get any meaningful information on them.
This doesn't mean they are bad cameras, some are quite good. But the problem is that the buyer is pretty much on his/her own when it comes to deciding to buy or not.
Basically, I would suggest that if you get a good price that is significantly lower than an equivalent 'name brand' camera and you are willing to take a bit of a chance, go ahead and buy it. I doubt you will get a BAD camera, and it might be very good.
On the other hand, if the Vivitar price is close to the name brand price, I would probably suggest going with the name brand. Like the old saying, 'Better the devil you know than the devil you don't know'.