This is all the terms has to say on that matter:
Addresses assigned to Customer by Hurricane may only be used in association with the service under which they were assigned and only while a Hurricane Electric customer.
The wording is a bit vague. What does in association with cover? I expect that every host and network you give addresses out of the HE provided address space will still route some of its traffic through the tunnel service, so the addresses would have been assigned in association with the service. The terms don't require you to have every single packet used with those addresses go through the tunnel service. Packets between two hosts on your LAN with addresses out of the same prefix assigned from HE, will never reach the tunnel service.
Enough about the wording of the terms, lets for a moment consider what the intent of that sentence might be. I think what that sentence is mainly supposed to disallow is the following situation. You register a tunnel and get a /48 assigned. But instead of using the tunnel service at all, you publish that prefix through a BGP peering, which could in theory reach all of the world. Being a more specific route than the one published by HE, it would attract the traffic. Such usage would clearly be a violation of the terms. And if that's how you want to use the address space, then you should be getting address space from a RIR, not from HE.
So I have given one example, which is clearly permitted, and another which is clearly not. Your question is about a setup which is somewhere between those two extremes. It would be nice with an official response about where that line is drawn. There are two questions that seem important in answering the question about which side of the line you are on:
- Do you have a tunnel to the tunnel server?
- Are you advertising the addresses through BGP?
If the answer to those questions are, yeas you do have the tunnel, and no you are not advertising the prefix through BGP, then I cannot think of a reason for HE to say you are on the wrong side of the line.
The traffic that goes through the peering would never touch any of HE's systems, and as such I'd say it should be outside of the scope of the agreement. And apart from the one sentence mentioned above, I couldn't find anything in the terms that would apply to your setup.
I don't know if you would intend to use BGP for your peerings, and I think HE will consider that important. Even if you don't intend those prefixes to leak outside of your peering, there is always a risk of that happening by accident.