A lot of hikers carry denatured alcohol for cooking. Is there any risk to using it as an antiseptic for cuts and lacerations?
No, it is not safe to use denatured alcohol for two good reasons:
Denatured alcohol refers to a class of ethanol produced for industrial uses that has been "denatured," which essentially means "made undrinkable" by mixing other compounds that are toxic or unpleasant to humans. The thing is, you, as the consumer, have no idea what exactly was mixed in. Different denaturing agents have different skin toxicities, none of them are pleasant, and some of them are known mutagens. Many countries also require denatured alcohol to be dyed to help prevent accidental consumption.
Any modern wound management training recommends against using alcohol of any kind as an antiseptic. Although it does kill bacteria, pouring alcohol on a wound also kills perfectly healthy flesh which disrupts the healing process, can result in longer heal-times, and result in higher susceptibility to infection down the road.
Best treatment for a wound: wash thoroughly with soap and drinking water then bandage appropriately (more thorough details in an answer to How could I treat scrapes outdoors without a first aid kit?).
I'm a physician. High proof alcohol – be it ethanol or rubbing – causes osmotic bursting of cells – like distilled water – and hurts like Hell. It is only suitable for surfaces, or intact skin. Even peroxide is harsh, if you use over 3% strength.