Yes if you do it manually, but not with the plugin they’re using. In their demo, they’re using the Simple Social Icons plugin created by StudioPress, but the Snapchat icon isn’t available with the plugin just yet probably since it just started becoming popular. So you’d have to manually add one in by finding the image you want and adding it to a text widget –
<img src="LINK_TO_YOUR_IMAGE.jpg">
I would contact StudioPress or one of the guys that created the plugin and ask if they’ll add it in since a lot of people are using the app now.