Not exactly (you're using 289.94 MB for that site by the way). DreamObjects' limit is 7T right now, IIRC.
In order to create the backup, the plugin has to check all your files and combine them into a zip. To do that takes PHP memory. When you run out, or when the process takes 'too long' (3 minutes right now), it stops.
So it's not that DreamObjects has a limit, but that your server has a practical limit of not letting commands run forever. This is a good thing in general (stops your neighbors on the server from using up all your CPU) but highly annoying for the plugin. I've been experimenting with making it support larger files, and not take as long to combine them, but basically the click-once-and-go method, where one command makes the zip, just isn't working. I'm going to have to break it out into multiple calls, so each one takes a shorter amount of time.
Theoretical upside: Larger sites will work perfectly.
Downside? The whole backup process will take longer.