At this time Showit doesn't have any client gallery functionality built into the platform. You can create +sites to display your clients images beautifully if you so wish, but it is for just that, display, it wouldn't be a solution for delivering images to clients.
At this time Showit doesn't have any options for direct integration in the platform with third party client galleries like those listed above. However you can absolutely link out to those galleries. You can use our URL click action link type to link directly to your client galleries from your Showit site.
Here is another great option: CloudSpot Galleries + Showit