Can RVCT 2.0 co-exist with ADS or RVCT 1.2 ?

Yes. They are installed into different directories, and have different environment variables e.g. RVCT20INC v. ARMINC, so there should be no conflicts with include files or libraries. You will, however, need to take care with the paths to the tool executables themselves. For example, the default path to the ADS executables is:

  C:Program FilesARMADSv1_2Bin 

and for RVCT 2.0 is:

  C:Program FilesARMRVCTPrograms2.0<build number><platform> 

RVCT 2.0 requires a new license key, however, the RVCT 2.0 license key for e.g the compiler, will also enable earlier compilers.