Last three years for Wheeler:
2008: 3.12 ERA, 0.99 WHIP, 7.2 K/9, 142 ERA+, 4.49 FIP, .202 BABIP
2009: 3.28 ERA, 0.86 WHIP, 7.0 K/9, 133 ERA+, 4.48 FIP, .203 BABIP
2010: 3.35 ERA, 1.07 WHIP, 8.6 K/9, 118 ERA+, 4.11 FIP, .243 BABIP
Consistently low BABIP the last three years, so hopefully that continues as opposed to reverting to the mean. His career BABIP is .285. Bill James projects a 2.87 ERA, 1.11 WHIP, 8.04 K/9, 4.19 FIP and .255 BABIP.
He's not the primary setup man or even the secondary setup man, so I'd say this is a good deal. It seemed the Sox were not very interested in Fuentes or at least the money and years required to get him, so I'd rather get a quality righty than a mediocre lefty.