1), Yes it is a general concern because your system won't work as you intended and getting air into systems on a continuous basis leads to two phase flow, potential for air locks, surges and unstable flow. However for PD pumps per se, they can generally handle some entrained air without major problem as micalbrch notes. Its generally not too difficult to put in an anti vortex inlet header or even just expand the inlet to reduce inlet velocity.
2) Not come across this before, but looked it up and seems to be the business for pump inlets (I learnt something new...). As said there are other easy things you can do apart from submergence depth to reduce or eliminate vortices such as bigger inlet, orientation of inlet, inlet guide vanes, end plate and side entry slots.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way