As far as I know, and as far as I can discover this information is not available in the API.
However it can be discovered with a little work, well at least in .Net is can
Here is a one line pice of C# .net code
string licenceFilePath = Application.UserAppDataPath;[/b]
The contents of licenceFilePath for my installation running Windows 7 is
C:\Users\pchudley\AppData\Roaming\Sparx Systems Pty Ltd\Enterprise Architect 9\9, 0, 0, 908
If I change version of EA to say Version 8, the same line of code yields
C:\Users\pchudley\AppData\Roaming\Sparx Systems Pty Ltd\Enterprise Architect 8\8, 0, 0, 864
Split the string using \ as the delimiter and the last entry in the string [] will contain (for the first example) 9, 0, 0, 908
That is the version and build number of the EA version that is running your add-in.
Hope this helps in some way.
Cheers
Phil