There is a plugin for poser which converts the materials for octane and allows you to adjust the materials and then render directly in Octane (available on the Otoy site)

If you want to use the standalone Octane render, you can do an OBJ export and import the OBJ in Octane. It will make it a lot easier if you do a "Colllect Scenery" to a new folder to get all the textures in one location and store the export OBJ there. If not, you may have to locate and load each of the textures manually in Octane.

The plugin is a lot easier