Dish did my install back when they put in my 622 with a DPP44 and I never had any caps on open ports. Even the auditor did not require them when he came by and made them re-do the grounding.
Yeah, on my four-Hopper setup, DPP44 + DPP33 stack, no caps on the two unused port 4s on the DPP44 nor the mostly-unused power inserter receiver port. No issues at all. All unused ports on the two duo nodes are capped though. Maybe four switches stacked are just more sensitive to it.