Well, let's look at where Nolan's defenses ranked:
1993 Giants -> 5th, 12.8 Pts/gm, 291.4 Yds/gm
1994 Giants -> 11th, 19.1 Pts/gm, 309.4 Yds/gm
1995 Giants -> 17th, 21.2 Pts/gm, 330.8 Yds/gm
1996 Giants -> 14th, 18.6 Pts/gm, 315.4 Yds/gm
1997 Redskins -> 16th, 18.1 Pts/gm, 314.4 Yds/gm
1998 Redskins -> 24th, 26.3 Pts/gm, 334.6 Yds/gm
1999 Redskins -> 30th, 23.6 Pts/gm, 356.6 Yds/gm
2000 Jets -> Tied 10th with PHI, 20.1 Pts/gm, 301.2 Yds/gm
2002 Ravens -> 22nd, 22.1 Pts/gm, 334.6 Yds/gm
2003 Ravens -> 3rd, 17.6 Pts/gm, 271.3 Yds/gm
2004 Ravens -> 6th, 16.8 Pts/gm, 300.2 Yds/gm
Hmm. Besides the Ravens years it seems like his defenses have a trend of regressing. However, since those are his early years and now he has some head coaching experience, dealing with adversity and bad situations in which he was in control, I think stepping into a defensive coordinator role again might be benificial. We'll see though.