Here is an example of exporting Ri Attributes (e.g. Ri Round Curve) to an Alembic File for reading into RenderMan for Maya.  

• Add an AttributeCreate node.
• Name it as how it is named in RenderMan for Maya, e.g. rman__riattr__dice_roundcurve.
• Set the Class to Detail.
• Set the Value expression to the Ri Attribute (e.g. ri_roundcurve)

You can download this example here: curves_alembicattr.hip

When you read the alembic file into RfM, you will see the Round Curve attribute with the setting from Houdini.