Q: How to copy smtiles tiles to MongoDB?

A: No, you can’t. But you can use the tile updating to achieve indirectly. The tile updating URI:
http://{IP/domain name}:{port}/iserver/manager/tilesetupdatejobs 
But first you need to have a same map tile set in MongoDB. It can make the first grade scale tiles to MongoDB. Then update the smtiles tiles to the tiles in MongoDB.