The short answer is no, at least not through any legitimate channel, and the tablets themselves are designed to prevent it.
Facility-issued tablets, whether through JPay, GTL, or another provider, are not connected to the open internet. They run on a closed network that is controlled and monitored by the facility and the tablet provider. The applications available on those tablets are specifically approved and installed by the provider. Social media platforms like Facebook, Instagram, and Snapchat are not on that approved list and cannot be downloaded or accessed through the tablet's system. The network architecture simply does not allow it.
What inmates can do on tablets includes messaging through approved platforms like JPay email, music, educational content, games, and other applications that the facility and provider have specifically approved. Every message sent through the tablet system is logged and can be reviewed. There is no private channel through a facility tablet.
The workaround that does exist is contraband smartphones, which are a completely separate issue from the tablets. Someone with a smuggled phone has access to the open internet and social media, but that has nothing to do with the facility tablet and carries serious consequences if discovered.
So to directly answer the question: no, they cannot use the facility tablet to get on social media, and the guards do not need to be watching in real time for this to be impossible. The system is built so that access does not exist in the first place.