You absolutely can publish your book with CreateSpace and NOOK at the same time. Each print version needs its own ISBN.
I wrote to B&N about this exact issue, and this was their response, emphasis mine:
Please note: Each NOOK Press print book needs a new ISBN that has never been used on any other print platform. If your print book is currently available for purchase at BN.com or any other retail platform, you cannot use that same ISBN again on the NOOK Press print platform. You may elect to receive a free ISBN through NOOK Press during your set-up process (resulting in your Publisher Name being designated as “NOOK Press”) or you may want to purchase one on your own, which will enable you to set your own Publisher Name.
1) According to Bowker, the main place to buy ISBNs in the U.S., you do need an ISBN for an e-book. This has changed from a few years ago, when you didn't.
The purpose of the ISBN is to identify one specific version of a book. If you wish to have a hard bound copy, a soft bound copy, an ePUB, a PDF, a MOBI, or even register a new version, you will need a unique ISBN for each version. This allows retailers to help the customer understand exactly which version of a title they are purchasing.
2) Note that ePUB and MOBI are two different e-book formats, and Bowker specifically calls them out individually. Therefore I would say yes, each e-book format (Kindle, NOOK, iBooks) needs its own ISBN the same way hardback vs. paperback needs a separate ISBN.
When you buy your own ISBN from Bowker, you can either buy 1 or a 10-pack (or more, but a self-publishing writer usually only needs 10 at a shot). Therefore, since you already have the 10 numbers, I would go ahead and assign each e-book format its own ISBN.