If you know what to look for - by looking at it through a fairly powerful microscope.
Only if he got someone pregnant or if he leave a sample at the doctors.
The pre-ejaculate fluid produced by the Cowpar's gland (sometimes called pre-cum in slang) can contain sperm cells. Not a large quantity, but it can contain sperm. Hence, it is technically possible...
It refers to good motility; the sperm swim well.