You certainly won't break anything doing it that way.. But I think it depends on how you want to manage your reporting. If you do want to go that route, you could just add the advertising costs into your overall content program costs, but the problem there for me is that those costs are above and beyond what it took to create a piece of content and can skew your ROI reporting.. I prefer to report on ROI for the content itself, and prove whether the advertising venue was worth it by having it's reporting data trackable via a separate program.
In my mind a "channel" is the method programs use to progress a lead to "engaged success." We use other tags to delineate business verticals, content type, etc., and the channels as more of an overall indicator of input method... So Content, Digital Advertising, Contact Us, etc.
If it doesn't look cool, you're probably doing it wrong.
Do you see any concerns around using the same channel tag but utilizing a Tag (Maybe name Traffic Source) to separate regular content from digital advising? .png)