We are currently using ExpressionEngine v2.1.3 with Discussion Forum 3.1.2.
Will eeBootstrap work with this version of EE?
Please advise and thanks!
Looking at the changelog official website nothing refers to templates except for version 3.1.14 (https://ellislab.com/expressionengine/user-guide/add-ons/forum/forum_update_notes_3.1.14.html).
In any case I would not guarantee perfect operation with the version you have.
From my point of view I would recommend you to upgrade the forum to the latest version.