Why not check the page size of the pdf to see if includes bleed? If it is .25 bigger than the trim size then the excess can be used as bleed as long as there is enough room to keep copy from trimming.
Kind of, not really. It's a real tricky thing to detect. We can detect that objects are within a certain distance of the trim edge, and under certain conditions we can extend rectangles into the bleed area. But it is limited in its effectiveness. Better than doing nothing, but not 100% reliable. So yes, kind of, sort of sometimes.
just open the pdf in acrobat pro, you don't even need pitstop to do this, then place your mouse in the bottom left corner of the window and the size will pop up. You should be able to tell if it has a bleed this way- as long as you know what the final cut size should be.
Detecting "effectively bleeding objects" in a meaningful and automated way is kind of the holy grail of preflighting. No one does it correctly all of the time. Still need a human for that!