The main purpose of iNat is to build a community, and while it’s great you’re helping others, photos posted to iNaturalist should represent your own experience. So I would say definitely do not use a second account for this purpose. Encourage them to join iNat or, if they don’t want to do that, there are a ton of Facebook groups and people on Twitter (yes, those platforms have their downsides) that are great for IDs. And yes, there is also the fact that photos and observations are only credited to the owner of the account.