Hi Steve,
SAP does only test SAP NetWeaver on SQL Server enterprise editions. Therefore, we do only support Enterprise Edition. That is very clear on SAP Note 62988. That is, Enterprise is the minimum edition we support, as old versions like SQL Server 2008 has a Datacenter Edition, which has more features and support additional resources etc.
What happens to the Developer edition:
Even with Microsoft statement that it has the very same features of Enterprise Edition, SAP will not provide support on any SQL Server edition that is not Enterprise (or a higher edition). Even if Developer edition has the same features, it is not Enterprise Edition.
Now, it is just about the support. I can't comment on the Licensing, because from SAP perspective, customers that acquired SQL Server from SAP, does not have to care about this (using a developer edition), because they have a runtime licensing, that is, they can use for all systems in the landscape (DEV, PROD, QA) as they want. Even if they want to setup a DR database they don't need additional licenses.
I think that you should first contact Microsoft and ask them whether the usage of this license with SAP would be supported (e.g. compliant with Use Terms).
Consider also that you should have a contract with Microsoft in case you have not acquired SQL Server from SAP, as per SAP Note 398136.
Best regards,
Luis Darui