There was strong evidence a few months ago that if you twist their arm,
Dell *will* do an Opteron system for you - somebody at Dell made a mistake
with the Web site and it appeared as "available" for a couple of days.
It's not really so much that they will sell you an Opteron *system*
(though they might on a contract-basis, ie if you contract Dell for a
super-cluster of 1000 Opteron servers, they'll probably be more than
happy to rebadge some servers for you), but a few months back they DID
sell Opteron processors.
The reason for this is actually much more simple than many people
believe. Dell (and HP, and IBM, and all other big OEMs) will sell you
a support contract for damn near anything if you pay them enough money
(hint: do a search on "multivendor support"). If you're willing to
pay the big bucks, Dell will provide you with support for your HP
DL485 Opteron server. As such, if one of your chips goes bad, Dell
needs to have a way to get replacement Opteron processor to you.
The reasons why you would want Dell supporting your HP server (or vice
versa) are a bit more complex, but all basically related to having all
your support contracts handled by one company. ie your company might
have 300 Dell servers and one odd-ball HP server... rather than having
a whole other contract with HP for support for that one server you
could just role it into a big, company-wide contract with Dell.
One-stop shopping.
Of course, the moral of this story is that it's quite a different
story to have some Opteron processors available to people with
contracts vs. selling a full-fledge Dell-branded Opteron server.