"...if the oil pressure were low, besides checking the dipstick, how would I know if the oil pump was defective?"

It seems that you're asking, "If I have low oil pressure, how can I tell if it's due to a bad pump?"

First, you need to determine whether or not your pressure is low. To do this, you need a gauge installed in place of the oil pressure switch. Then you can watch the pressure as a function of temperature and engine (pump) speed.

When you have a worn engine, you typically see good pressure with cold oil (viscous oil), but the pressure drops as the oil gets hot. Also, you'll see low pressure at idle but increasing with increasing engine speed.

If the pump is bad, you'll see less increase with engine (pump) speed increase and less drop with increasing oil temperature.

Keep in mind that oil pumps rarely fail. I had about 350k miles on an '82 with the original engine and pump -- and never had any indication of low oil pressure.

"What are other symptoms of a bad oil pump?"

No oil pressure would be an excellent sign of a bad pump.

"How would a defective oil pump cause changes in the dipstick?"

No effect. Oil level (if that's what you mean by dipstick) and oil pump condition are independant. Your engine (oil pump) will continue to produce the same oil pressure with increasingly low oil until the pickup starts sucking air.
--
Don Foster (near Cape Cod, MA)