I'm kind of surprised at some of the answers given here. I'll respectfully dispute the idea that hair transplant surgery does not cause any bruising. It doesn't, as a regular side effect, but the honest truth is that it does sometimes create bruising, and it is not a rare occurrence. The question then switches to one of frequency. How often does it cause bruising and this depends on the clinic and how aggressive they are with dense packing, which is the leading cause of bruising during recipient site creation. The scalp will always be somewhat pinkish for the first while after a surgery but when you see dark areas that stand out from the overall consistent appearance, that is most likely caused by bruising.
Is bruising a bad thing? Not necessarily. It just depends on the severity of the bruising and how large of an area that it affects. If it is large then you have the potential for necrosis.