If you rent an apartment, even though you don't own the building, you have "rights of tenant in possession". Basically the apartment is "yours" and you have rights. If a search warrant is to be served to search your place, it gets served on YOU, not the owner of the buildng.
If you rent server space, like a rack in a datacenter, that space is "yours". So should the search warrant have been honored?
I read the article, they do say "colocation"; besides which, XO Communications does not rent servers as far as I know. So that seems to point that they were renting the physical space that their servers are in.
Would it make a difference if they were just renting a partial rack, or a full rack that goes all the way down to the floor and is enclosed? I don't know ...
The contract I signed, had a clause that said if they had to move me somewhere else, they would pay all costs of doing so. I don't know how standard a clause this is.
I rent a furnished appartment, and while the company that owns it would never touch it without my permission, the contract is very specific about it being this building, they would never say "mind moving next door?" whereas with a rack in a data centre, not only does the contract not specify exactly where the rack is placed, it makes very little difference about it's exact location.