I have not done any OpenXml, but the download page for OpenXml is clear that 1.0 is compatible with office 2007. The download page for OpenXml 2.0 does not specify any outlook versions at all.
If we only have office 2007 or need to be office 2007 viewable/compatible and I'm looking at generating charts in outlook from c# code, can I proceed to OpenXml 2.0? Are there issues or is it full compatibility?
This download page says that Word 2007, Excel 2007 and Powerpoint 2007 are supported by the Open XML SDK 2.0. Just take a look at the Overview section. I don't believe that Outlook is supported since I have not seen any documentation on it anywhere.
Also, if you go to the documentation for the Open XML SDK 2.0, you can see here that they only have classes for word processing, spreadsheets and presentations.