I can't find hospitalizations broken out by underlying illnesses, but if among each age bracket we assume the % of deaths associated with underlying illness holds as the % of hospitalizations associated with underlying illness, then we get a "healthy under 65" Hospitalization Rate of 0.3% to 0.5%.

Under 65:

7.4M people

1.55M infected

26,000 hospitalizations

4,548 "healthy" hospitalizations (16% of deaths under 65 have no comorbidities. Using same rate here).

800k-1.2M infected w/o comorbidities depending on "healthy rate"

4,548 / 1M = 0.45%