The differences in assessing the output of a proportional odds logistic regression and an ordinary least squared regression are analogous to the differences with logistic regression (discussed at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1065119/) . Basically, you get the ammunition for applying test statistics, which it's up to the analyst to decide which are appropriate for the data and purpose, which is often domain-specific.
If you want to take a deep dive, a standard text is Applied Logistic Regression, 3rd Edition
by David W. Hosmer Jr., Stanley Lemeshow, and Rodney X. Sturdivant (2013) (Wiley).