How do you know it has vacuum?
And when you say that, do you mean the crankcase has vacuum? Or the oil system?
How do you know it has no oil pressure? Did you double check it with a gauge?
I can't think of a single way that you could have vacuum on the oil circuit...... I'm hesitant to say, it's impossible. (Because I've seen so much that shouldn't be, that was.)
If your talking about the crankcase being under vacuum...... how much? The crankcase pulses... if you put your finger over the vent it you will feel it suck slightly... but should build pressure after a short time.
Need some answers to above questions......