Sure! If you have a long list of names accepted by POWO that you need for your checklist, you might be able to get them added en masse by emailing help@inaturalist.org. (I make no guarantees whether they would be able to prioritize something like that.)
For a shorter list (couple dozen maybe), probably best to follow the standard practice of going to the parent genus page (or family if needed), flagging it for curation, and asking the curatorial team to add the relevant taxon or taxa.
Either way, for any names not accepted by POWO, those would need further discussion first to see if there is consensus for a deviation from POWO, before being added to the iNat taxonomy.