I am going to post assuming that there is a transformer present and that the secondary is isolated from the primary.
I don't know what the NEC requirement is for not letting a system float with respect to earth ground, but lets assume that 48v is above that requirement. Then your connection is correct. It is also correct to unhook the negative side and ground the positive side although nobody in their right mind would do that as everyone expects the negative to be tied to earth ground. Assuming that we are not wanting to protect against transients on the low side, the only reason to do that is for safety (excluding noise considerations).
Now if the two sides are not isolated, then there is no connection required because the secondary is already tied to earth ground because the primary is.
Now if 48v is below the NEC requirement for floating systems then you don't have to do anything, but I would probably ground it anyway so that it will pop the breaker in case the other side does come into contact with earth ground or chassis.
Oh, that is not with a resistor of any kind. That is a direct wire connection to the chassis. If there is a 10M ohm resistor in there, then the breaker will not pop, and you will have the situtation of a hot wire touching the chassis in the first place. The addition of the resistor is a BIG NO. USE A DIRECT CONNECTION WITH A WIRE! The 10M ohm resistor is dangerous.
For ground loops, tie both grounds to the same point on the chassis. Ground loops farther down stream on the 48V supply is a different story.