They should. 6s fully charged is 25.2v, and 20 NiMh cells fully charged are around 27.5v. 20 NiMh cells nominal are 24v, 6s Lipo is 22.2v. As long as you get a controller that can handle the amp draw, it will be fine :).
SH Z-Car, Custom Crawler, 8s Savage, 12s XTM XLB 1/7 buggy, 4wd 4-link rear/IFS Pro4 truck, Custom Hyper 10 Short Course, Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz