Can I sink a hot water copper pipe into the ground and keep the heating functionality
The hot water baseboard heating will be heating the room mostly due to radiative surfaces that conduct the heat out of the water pipe and into the air of the room. For this to work there needs to be allowance for the air in the room to naturally move from the heater area and into the room.

If you cover it up it will not be heating the room in the same way.

If you end up having to bypass the hot water piping beyond the area where you are now placing cabinets you will have to arrange for alternate radiative devices to be installed elsewhere in the room so that the heating can be effective.