Yes, like the iPhone, the camera shutter sound is mutable using the system mute setting.
With regards to iPad 4K. In general, prior to the iPad Air 2, iPad cameras maxed out at 5MP (vs. iPhone's 8MP) so the higher resolutions didn't really approach 4K. In practice, the iPads I tested with were incapable of handling video encoding of anything larger than 1080p. I have not tested with the iPad Air 2 and I don't know if/when I will be able to. I currently have no plans of acquiring one. If you have an iPad Air 2 and are willing to test potentially several iterations of TimeLapse test versions, perhaps we can work together to see if it works.