I chatted with aparicio last month about exactly this question and appear to have found the answer I needed!
aparicio:If you use it only for email more than likely you will have no issues using an iCloud account on Snow Leopard. And you can upgrade the account by just going to an Apple Store or a best buy and using the computer there. None of your data is actually stored on that particular device and it only takes 3 to 5 minutes tops to do so.
Me: Ah, so I go to the genius bar and they can help me or I do it straight on some demo model in the store?
aparicio: Correct.
Me: And you're telling me that after the conversion I can still receive and send emails via that acct. and won't be forced to upgrade to Lion as long as email is all I need from iCloud?
aparicio: Correct.
aparicio: But if there is ever an issue down the line you would not be supported until you upgraded to Lion.
Me: That sounds like a viable temporary solution that will take me beyond the June 2012 date. You keep telling me about the lack of support. What do you mean by this? The acct. should work like all the other apple accounts, right? I've never had an issue with it where I received support.
aparicio: I just want you to be aware that even though it will work it is not supported by any Apple technical support unless you have the latest software which is Lion.
Me: what kind of support are you talking?
aparicio: And it will work like all other Apple accounts so if you never had an issue more than likely you never will.
aparicio: Apple Phone and chat support.
Me: Ah, ok. More like user support, not some behind the scene technical glitch at your end, right? Basically if I'm too dumb to use it kind of thing?
aparicio: Correct.