It is definitely total integration with your DAW. Or else you'd need to plug audio cables into your interface's inputs to hear the Virus through your audio interface's outputs, like you do with every hardware synth (which, incidentally, you can still do, if you want...Some people swear by this system giving you more "warmth" because of the inherent analog distortion. Personally, I think it's poppycock...
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Essentially, when you're using your own audio interface and the Virus in TI mode (i.e. VST plugin and USB connection only), the Virus acts exactly like a softsynth. The only difference is that the bulk of the computing is done externally (by the Virus engine) and not by your computer. Meaning that the virus won't take much computing power, unlike some of the more complex plug-ins.
Audio latency depends on your audio interface (and how powerful your computer is) and it has nothing to do with the Virus. Yes, of course it can be argued that USB 1.1 isn't exactly the fastest protocol in the world, but the Virus won't need anything real fast because it doesn't use samples.