Well, after assuming it was a bad idea to rely on DEX_ROW_ID never changing, it is now officially a bad idea; David Musgrave has spoken on the Developing for Dynamics GP blog.
As David explains, DEX_ROW_ID was added when support for SQL Server was added to Microsoft Dynamics GP but is not guaranteed to always remain the same. For example, a change to the table structure during an upgrade could result in the DEX_ROW_ID changing. As it isn’t a fixed value, it should never by relied upon in customisations, integrations or custom code.