Running a DHCP service on your gateway is not insecure, in itself. But it's also not the most secure option, either. Any network service can potentially lead to a compromise, if the service has a security vulnerability, or isn't properly configured.
The added risk would be pretty small if you take some basic security precautions:
- The DHCP service should only listening on the local, internal network.
- Research whether your DHCP server software has any known remote vulnerabilities. If you find any, consider switching to an alternative DHCP implementation.
- Patch/upgrade your DHCP server software promptly when security fixes are released.
- Periodically check the DHCP server logs for suspicious activity.
These are just the standard security practices that apply to any service, on any host. It's still possible that an internal attacker could exploit a zero-day vulnerability in your DHCP service, but that's the best guarantee you can get with any service.
But there's no universal answer to this question. Each person needs to weigh the risks versus the costs for himself and his organization.