In reply to Paul Schmidt.

Yes, you can specify the identity line.
In the section "A reference line for the Q-Q plot," the line is added by using the REFLINE statement in PROC SGPLOT. An identity line is
refline x=0 y=0 slope=1;
In the section, "Maximum likelihood estimates," the line is added by using the QQPLOT statement. In the case of studentized residuals, you would create a normal Q-Q and draw the reference line for N(0,1):
qqplot RStudent / normal(mu=0 sigma=1);