Is this a Speedmaster Service Dial on a 2998-2?

Well, it's certainly not an original 2998-2 dial. The -1 and -2 dials have shorter minute markers on the right subdial.
Whether it is a service dial or a dial of a later 2998 or 105.002 is hard to judge based on these pictures.

It's in a UK timed auction at the moment. The details confirm that it has an incorrect 321 movement from a later model. Estimate GBP 9,500 - 10,500 + fees. Interestingly, an A4 dial can be either flat or stepped.

Service dial, service H/M hands

It is a text book assembly in my opinion

Fortunately no one has bid the reserve.