If they contributed, they contributed. Does it matter that they did so because there is a demand for their VMs to run Linux, rather than out of the goodness of their hearts?
If they contributed solely out of their own business interests, and their contributions add nothing of value other than compatibility with Microsoft's proprietary software, and nobody who doesn't want to use Microsoft's proprietary software will see any benefit whatsoever from any of the changes Microsoft contributed to the kernel, then yeah, I would say it's fair to rate Microsoft's contributions to the Linux kernel lower than those of a company like, say, Red Hat.
Those stories a couple years ago about how "Microsoft is now one of the top kernel contributors"? Look at it this way: That's how much Microsoft had to change the kernel to make it work with Microsoft's proprietary VM tech.
Fair enough. Microsoft's contributions are as welcome as anybody's, provided it plays by the rules. But are you saying we're supposed to congratulate them for it? Hardly, I say.