I believe these are both meatspace identities.
Nick Szabo is a "former law school professor at George Washington University" according to Wikipedia.
Wei Dai has attended SIAI/MIRI workshops in person:
http://lesswrong.com/lw/ig9/outside_views_and_miris_fai_endg...
("Wei Dai" could be a pseudonym but if so I haven't seen him mention that on Less Wrong.)