Do graduate schools read your undergraduate application? If you apply to a university to be enrolled as an undergraduate, and are rejected, and then apply to the same university's graduate program, will they look at and/or take into consideration your undergraduate application?  Or is it considered irrelevant?
Irrelevant. 

Indeed, I suspect that in most or all graduate programs, those reading your graduate application do not have access to your undergraduate application, won't know that you applied to their undergraduate program, and would not care even if they knew.