Does Veryant provide a plugin to Eclipse or did Veryant customize Eclipse to be the IDE for isCOBOL?

Veryant provides both an Eclipse plugin which can be installed within any Eclipse-based IDE, and also the isCOBOL IDE, which is Eclipse with the isCOBOL plugin already installed.

The Eclipse-based isCOBOL IDE is for COBOL developers who are new to Eclipse or who want only to start with the COBOL development features.
Other features can be added through Software Updates in the Help menu.
The isCOBOL IDE can be downloaded from Veryant.com download page.

The isCOBOL plugin for Eclipse is primarily for developers who already use Eclipse and want to add isCOBOL IDE functionality.
The isCOBOL IDE plugin is listed on https://marketplace.eclipse.org/ under Languages.
You can add the isCOBOL IDE functionality using Veryant's update site URL http://support.veryant.com/eclipse from Install New Software (or Software Updates) in the Help menu.
Follow the instructions in Veryant's documentation in the isCOBOL IDE documentation under "Getting Started/Download and install isCOBOL Evolve". The plugin instructions are in the "other" section at the bottom of the page.