what is the data you are looking from using DAPI staining in cell cycle assay?
PI stains dead cells so it is used in cell cycle analysis,where as DAPI is used to stain both live and fixed cells.but intensity of staining is less.PI is preferred when compared to DAPI.
PI r DAPI staining will not give you the exact data.Better to use kit.If you are using kits the final analysis can be done by flow cytometry or fluorescence microscopy.
I would suggest you to go through Annexin V & PI as biomarkers for apoptosis .