Yes, you can do PhD after completing Mtech through BITS Wilp program , for that you have need to fulfill the eligibility criteria set by the college for which you are applying the Ph.D.
For some IIT Colleges I checked that they have minimum eligibility criteria of having 7.5+ CGPA in Mtech plus significant GATE Score.
For other colleges they have criteria that if you have published an IEEE paper then it would be added advantage and considered equivalently as GATE score.
Some colleges won’t consider part time BITS Wilp degree to take admission in Ph.D program.