Dear Peter,
I own both but I don't know exactly what you mean by related.
VSE is a VST instrument with its own propriety user interface, a very well designed one, in which you can load the samples. Opus is a sample library for which you need a seperate sampler application (like Gigastudio). I find the interface a step-up from the Performance Tool/Midi Router combination you had to use before (although I must say I haven't used Opus for long until I switched to VSE).
If you mean there is a relation between the samples in the two libaries: I remember recognizing many samples as they do sound the same so I guess they reused a lot of the samples (lets face it: the quality of the samples was never the problem, was it?
VSE is really meant to be run from within a sequencer so you really need a VST compatible (PC) or RTAS, AU (Mac) sequencer if you want to use it optimally. But it is also possible to run it standalone.
But remember that when you use VSE standalone, it has no built-in effects like reverb (coming from GigaStudio that was something I had to get used to) and there is no way to add other vst-plugins.
Vince