It is possible to use the REST API to publish models directly to MAS. However, you can only do so with properly formed DS2 code. Please refer to the MAS Programming and Administration Guide for additional information.
Most SAS Enterprise Miner models produce data step score code but they do not produce DS2 score code. As a result, you would need to do any conversion yourself. Unfortunately, I do not have any examples of taking this approach because it is not supported by SAS Technical Support. Since using SAS Decision Manager to publish the model to MAS handles the conversion process internally, it is highly recommended to use the SAS Decision Manager process.
I hope this helps!
Doug