The following theming functions are available in the OpenLayers 2.x module:
These themes are on the JS side.
This is the top level theming function for popups. It creates basic wrappers for the title and description in the popup. If you need to theme the output of the title and description variables, please see the PHP functions and the default available Views theme functions. If you wish to change how the popup bubble looks, then look at implementing a new popup behavior.
This is the same sort of thing as
Drupal.theme.openlayersPopup(feature) but for the tooltip behavior.