I'm assuming you refer to data centres (like Amazon) that configure virtual machines and rent out the capacity to users, and not using an in-house server with VMs configured.
That being the case, the fees that the provider usually charges is already based on a lot of factors such as expected processing load, duration of subscription, etc etc that have already been factored into the bill. Let's say, for example, you have subscribed to Company A's services and are guranteed up to say, 20% of the server's resources at all times. You going for an x32 guest and lowering some of the processing overheads to say, 17% will make the provider very happy for sure, but don't forget that you have already paid for that 20%.
If anything, you want to make full use of that 20% resources and get your money's worth out of that subscription you are paying.
X32 userspace can/should sit on an AMD64 kernel, so the AMD64 NVidia driver and the 386 flash player would all work just as they do now in 64-bit systems.
Except that you need 64 bit xorg (and dependencies) and a x86 browser (with dependencies) which would void the RAM saving for your graphics and the speedup for your browser. While the browser thing is a minor issue (just use a x32 browser as long as you don't need flash) the xorg thing is not, so you're better off with open source drivers.
//EDIT: Also don't forget that x32 programs can't use amd64 libs, like libGL.so, so the nvidia driver will force many things to x86 or amd64.