All that means is that those integrators paid Nvidia a big fat fee to certify their workstations. If you can get a full SMBIOS dump from one of those machines, you can probably fire up a KVM VM using QEMU with the relevant SMBIOS payload and it would just work.
Nvidia is well known for this kind of blocking in the drivers - they did similar things to block GeForce cards working in VMs, that was kind of why this thread started.
With regard to SLI you are wrong. Nvidia might be an "evil" company (they did ample of things to deserve this label, but you could say the same about probably any other company of sufficient size), but Quadro SLI certification has a serious background. It really is about protecting the brand reputation and thus protecting business opportunities and margins. It's not about earning money through certification fees...
Quadros in SLI configurations will often been used in numbers to power big (stereoscopic) multi-projection walls, CAVEs and similar installations, where targets for both performance as well as visual quality have to be met (performance especially crucial with regard to stereoscopic installations). Such installations cost big money (easily in the 6 digits, for stereoscopic CAVE installations far beyond 1Mio US$), and if something does not work as advertised/promised/demonstrated to the customer, all hell breaks loose...
Manufacturers of such certified workstations are almost always directly or indirectly involved in such installations (you know, big money, reputation...) and, when problems arise and the shit hits the fan, are usually able and willing to not only provide technical support via phone, but often also send technical support personnel.
Allowing such installations to be made out of random components opens up the risk for all sorts of problems with those installations, which for any technical support guy will be nigh impossible to fix in acceptable time due to the random nature of the chosen hardware configuration. How would you avoid such risk? Simple, make sure that random hardware configurations cannot happen... From the perspective of a "little" customer this might be hard to understand, but think of it like this: Big boys play with big toys, and when the toy is making trouble, then big boy gets very angry. Better make big boy not angry, otherwise you will get a bloody nose...