It's not possible to Passthrough keyboard and mouse still on 5.1. HID devices aren't allowed to be passed through.
Also if you go that route when you've already got a device passed through like a VGA card in your case or any passthrough device then you cannot actually edit the USB (or any) devices plugged into the VM without shutting it down first. So if you wanted to attach a USB Hard Drive or pen drive that would require the VM to be shutdown each time. This is hardly practical.
I don't understand why some cannot understand despite people saying many times why some people need this. It worked on 5.0U1, its now broken on 5.1. It seems strange that your defending VMware from fixing a bug in their software that they've introduced.
Personally from my reading I believe it's a bug which got introduced into the Linux kernel which has since been fixed in later revisions. So to fix this I think it requires VMWare to update the kernel or back-port the fix. This might be viewed as too risky for a small patch process as it could bring in other problems and would need to be heavily tested. I do accept that this functionality is probably only used by a small minority of their customers. So I don't actually think they will fix this on 5.1. I think the first time we might see a fix is in 6.0 at the earliest which is a shame. That is assuming they ever bother to fix this.
The problem in my opinion is that other hyper visors aren't quite up to the level I'd like in other areas to warranty switching when 5.0 U1/2 works perfectly. However if VMware doesn't fix this and the OS support of 5.0 falls behind I suspect KVM / Xen to have improved enough to make switching to them possible.