I asked DH support about something a bit like this a few years ago and they said OK, adding "We basically don't want our customers offering free file upload/download sites that put a heavy load on our servers. Your usage is specific to your business and won't be a violation of our terms of service."
The question is about the use of a web site to facilitate the transfer of information that is not itself part of what the browser sees or hears or plays - for example, high quality TIF files which are much larger than the JPG which would be shown on the web page. (UNSTATED but implicit in the question is, what about high quality video files which are much larger than the MP4 which would be shown on the web page.)
I think DH's policy is essentially pragmatic, and my understanding of it as applied to this kind of issue is that (N.B. personal opinion coming up)
If all the content is uploaded by you, and downloaded by N of your customers (thus the load being 1*N which is linear in N), then that should be OK for the time being and as long as your usage does not cause any statistics to spike
If content is uploaded by any of your customers and downloaded by any of them, then it would probably be not OK (since the load is N*N which is quadratic in N and could easily cause statistics to spike).