Online, safety cars would not work, as a lot of people will bew crashing out and short races will effectively be run entirely behind the safety car. Offline also, 2 lappers could get pretty dull with safety cars, not to mention a Nordschleife race...
iRacing has safety cars and flags for Oval racing rules and they work well enough online it seems. They don't have safety cars for Road races though but the flags are there (well, not a full black, just a speed penalty).
On other points - for blue flagged cars, I wonder if GT5 won't simply ghost them so the lapping car(s) can get by without some fool deciding to wreck other's races. Not realistic obviously, but without penalties for not yielding in game, I'm sure you'll get plenty of problems.
Finally, GTPSP has a pace car like this one, so I wonder if that means it'll be available via PSP transfer in GT5?
r.