Other than a noticeable change in attainable rate and SNR margin, I don't believe modems typically display the vectoring state.
However, the ASUS (when using TC Console) shows the vectoring state with 'wan adsl diag', and some reasonably good news is that it's looking likely that when G.INP is enabled on a circuit then it will work fine at full sync rate in comparison to the HG612 or ECI /* modems (as G.INP is most likely masking a compatibility issue with a good number of fastpath VDSL2 connections). Hoping ASUS will fix the actual problem in the end however, without me relying on G.INP to save the day.