It is a single cluster but I did not see anywhere in this post that we are reffering to a business edition. Since there is a sub already in the picture it would rule out this option in this case.
Steve,
If you read the SRND it is very clearly stated in there that a pub and sub is best practices. If you call TAC with an issue and they see that it is single server cluster, they will ask you to implement best practices (add a sub in this case) and if the problem exists after that you can open a new case.
Obviously this is ultimately your customers call. However in my case I would not do that for a customer without a documented acceptance from them and that they understand the implications involved.
I am not saying it will not work or that you will have issues, I just advice against it.