Works fine and is more efficient than running separate instances.
Here's mine running a GPU+FGPA+ASIC:
cgminer version 3.2.1 - Started: [2013-06-11 06:34:25]
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(5s):6.701G (avg):6.806Gh/s | A:3437 R:3 HW:0 U:23.5/m WU:95.9/m
ST: 1 SS: 2 NB: 11 LW: 15589 GF: 0 RF: 0
Connected to au.ozco.in diff 4 with stratum as user
Block: 001be5184832ccbd... Diff:15.6M Started: [08:52:15] Best share: 9.34K
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[P]ool management [G]PU management [ S]ettings [D]isplay options [Q]uit
GPU 0: 72.0C 3517RPM | 717.5M/717.5Mh/s | A: 401 R:0 HW:0 U: 2.74/m I: 9
BLT 0: | 396.6M/398.8Mh/s | A: 180 R:0 HW:0 U: 1.23/m
BAJ 0: max 42C 3.42V | 5.521G/5.691Gh/s | A:2856 R:3 HW:0 U: 19.51/m
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[2013-06-11 08:57:35] Accepted 3d0aba5c Diff 4/4 BAJ 0 pool 0