Thank you for using our services.
There would be no problem using OpenAccess that has different version on your computer on other projects. We have taken care so that there are no version conflicts. Other than that you will most probably be able to upgrade your OA version within Sitefinity just as with the RadControls for ASP.NET AJAX before we officially release an update/SP.
At least for now Sitefinity 4.0 is on a different schedule from the rest of the Telerik products. However we aim to at least keep up with the latest official releases of RadControls for ASP.NET AJAX and include them in our SPs, so this will also valid for 4.0
All the best,
the Telerik team