I'm not sure I agree with this statement. The repo market may not help or hinder corp debt directly, but I think it very much so effects corporate debt.
Corporations presumably get their loans from banks. What facilitates banks to make these loans? The Repo market. What happens if the repo market collapses / shrinks / endures instability? Banks most likely, would not be able to make as many loans and the rate for future loans would increase due to lower supply and higher demand.
On top of future loans, this could have a negative impact to current outstanding loans held by corps. I'm not 100% sure the terms of corporate loans, but if they have variable rate loans with banks, this shrinking of loan supply coupled with increased demand for liquidity would surely hurt some of these corporations.