So here's how it works:
Storage vendors sell array controllers, which are often "tuned" or locked to only work with a certain brand/firmware version of disk. The basic reason being, that they're selling support (and making a massive stack of money on that, and the disk sales.) If you stick in any old disks, there's no way they can sensibly follow the support side of things, and there may be seriously unpredictable results.
SAN vendors don't like unpredictable results, it looks bad for them. There'd be no way to stop the media (and that's who they're interested in) from saying "PQRST Storage went wrong causing massive data loss for XYZCorp", and not mentioning "Because they used uncertified disks".
See what I mean?
Basically, it's a lot easier and cost effective if you buy their disks, then you get their warranty, their support, and their coverage when it all goes to shit.
If you want to save money on disks, I think you're playing in the wrong pool. SAN storage is EXPENSIVE, and reliant on warranties, SLAs and support. If you don't want to pay for these, then you could build your own storage server, but you've only got yourself to blame when it all goes wrong.
With regards to your question about AoE, I googled, and came up with this https://help.ubuntu.com/community/ATAOverEthernet
Seems to do some of what you mentioned. I'm sure there are similar packages/tools available for other OSes. Not too sure on the Redmond bunch, though.
That said, I've not used any of the linked materials, nor have I played with AoE, so YMMV.