Apparently, there are no "service-specific terms" for Cloudflare Tunnel, so the only ToS for that service would be the "main" terms (i.e. the Self-Serve Subscription Agreement)[0].

Therefore, as long as you comply with it (especially the sections 2.2.1 and 2.7), you'd be fine. There are no explicit constraints regarding content type, just on what the content itself is or represents (e.g. illegal stuff).

Disclaimer: I'm definitely not a lawyer.

[0] - https://www.cloudflare.com/terms/