Are you sure the data isn't coming through? Vertex color data is stored in map channel 0...which should be exported with the Alembic data, although in an auxiliary map channel (and labeled as such in the .abc format).
The Alembic exporter should be able to export all present UVW channels (in the latest builds only - previously it was limited yes, but not anymore)...if you send me the file I can take a look to see if the data is being exported properly in all channels.