We’re using an external RHEL server to run DHCP for the campus, so DHCP isn’t hosted on the FOG server. We confirmed in DHCP that the redirect lists undionly.kpxe as the filename. Thanks especially to @Sebastian-Roth for suggesting trying the realtek option. We switched filename to realtek.kpxe and the laptop is booting!
For fun, we tested booting two Dell desktops and two HP desktops after the realtek change. The Dells boot perfectly, while the HPs now having the same issue the laptop had (i.e. DHCP failed). Looks like we’ll use the realtek file to take care of this laptop, then change back to undionly for our general use.
Thanks for all the help!