Here's how I see it. Vmkernel has a driver API. It's documented, versioned, comes with a ddk and has drivers written directly to it.
As we all know, Linux basically has driver apis. They are not as explicit as the vmkernel driver apis; they are not versioned and deliberately unstable - but if you've written a line of kernel code you know they are there.
Now it seems it is OK to ship a binary blob driver that links against Linux driver apis. Nvidia, ati, lots of arm type boards and now zfs. I say seems because, well, so far everyone has pretty much gone along with it. In some of the comments on zfs, I see people go as far to say that the Linux driver APIs are tacitly considered lgpl (ie. similar to why you can ship a binary against glibc - although obviously glibc has made the exception explicit)
Can I do the reverse? Implement a GPL licensed wrapper that converts the Linux driver API to one provided by a binary blob (ie. what vmklinux does talking to vmkernel) and thus use the drivers?
I don't know, I think it's a good question to find an answer to.