I've seen conflicting reports on whether or not MEM Non-essential Amino Acids is needed as part of the complete media for HEK293s. I know we grow HEK293Ts in the lab without it.
As far as I know, NEAA are used to inmprove the cell growth and viability. However, if your lab is used to culture the cell line in absence of NEAA, I would not change the protocol unless needed for a specific reason.You may compare the MEM in use and NEAA formulations to find out what are the missing NEAA in your culture medium.
HEK293 are generally easy to grow and I have grown them with and without NEAA. Generally I go by the protocol that the lab I am working in is using so that my results are more comparable to the previous ones. If you are setting something new with them you could go either way I suppose.