Google XML Sitemaps plugin and Image Sitemap Pro do have some issues on WordPress Multisite installation. This does not mean you can not use them together.
If you are using Google XML Sitemaps plugin on multisite then my plugin may not create sitemap.You may get 404 error if you try to access sitemap-index-image.xml.
The issue can be resolved easily with below work around.
Install and configure the Google XML Sitemaps plugin.
Install and activate Image Sitemap Pro plugin.
That’s all. Both plugins should work fine.
You should deactivate and activate my plugin if you are deactivating and activating the Google XML sitemaps plugin. The technical reason is that Google XML sitemaps plugin wipes out the rewrite rules created by my plugin. So Image Sitemap Pro should be activated last.