The current release of the LiveLink plugin for Maya does not have support for custom curves. It also does not support Maya 2015.
I have created a patch that adds support for Maya 2015 and user defined attributes on the root joint. Compiled binaries are included in the repo for 2015. For 2016 and above you have to compile the plugin yourself.
Pull-request created on Github here.
Supports 4.22 and 4.23. The 4.22 plugin is deprecated for 4.23, so it is not recommended to use that combination as Epic replaced how curves are replicated.
- Maybe add support for blend shape curves. You can still replicate curves by adding them as attributes on the root joint. Drive the root joint attribute with the blend shape value.