The main pirating route at the time (a device (oh which there were several) that sat under the N64 and had either an Iomega Zip drive or a CD drive for holding ROMs), had a port for inserting a real cartridge to use its lockout chip.
As far as Nintendo's concerned, it is. Their method of piracy prevention at this point was putting a lockout chip on every cartridge, and attaching their license fee to the lockout chip. Your homebrew cartridge needs one too.