That is a return line for the oil going into the vacuum pump, it is not under any pressure, so when you transferred the vacuum pump to the new alternator you either cracked the line or the vacuum pump itself came apart and was not put back together correctly, as I recall there is an O-ring in there that could come out of its groove.
You can see in this photo that the hose is held on with clamps.
Remove your hose, go to the parts store and look thru there inventory till you find something the right size with the bends in the right place that you can make work, if you have to, you could likely use a straight hose and bend it, but it gets hot down there, so find something close if you can.
You need to figure out for sure where the oil is leaking from, it could be just a loose clamp also.