Tourist visa exit flight booked but planning on ground entrance at border

Hello I am an American trying to apply for a tourist L in Hanoi with no invitation as a guest in china and am curious for the guidelines if I submit my exit flight information only and tell them I am planning on making crossing the border from Vietnam via bus and not airfare, is this allowed? All of the requirements I am seeing is that it must be a round trip ticket in and out, in my case would two separate flights one in and the other out suffice if border crossing is not allowed?