Hello, my understanding re the implants is the same as yours.
My Husband Kris has had ongoing Dental issues post his radiation and consequent salvage surgery. The Head&Neck oncology Dentist gave us the same information that you have. Implants would never be an option. He also advised against dentures for the same reason - reduced blood supply and high risk of both osteoradionecrosis and recurrence of cancer.
Here in New Zealand it seems we have limited to no options. Maybe someone from the U.S.can better guide us here.
Tammy

Caregiver/advocate to Husband Kris age 59@ diagnosis
DX Dec '10 SCC BOT T4aN2bM0 HPV+ve.Cisplatin x3 35 IMRT.
PET 6/11 clear.
R) level 2-4 neck dissection 8/1/11 to remove residual node - necrotic with NED
Feb '12 Ca back.. 3/8/12 total glossectomy/laryngectomy/bilat neck dissection/partial pharyngectomy etc. clear margins. All nodes negative for disease. PEG in.
March 2017 - 5 years disease free. Woohoo!