If there is something in your background that causes you to be rejected, it's difficult to see how that would change if you attempted to enter through a different employer. What scenario do you have in mind?

Just in case if employer GHI failed to provide document in response to 221G and Visa got rejected. In this case does my petition filed by GHI supersedes DEF ?

If DEF employer wish to proceed with H1B process after GHI petition got approved does he again needs to file transfer ?