Four M10 Grade 4.8 bolts have a combined yield load of around 7.2 Tons.
This is before any tightening torque has been applied, and as Marnus points out, the tightening load effects how much strength is left for recovery. It is however very difficult to determine the tensile load induced in a bolt due to tightening, because there are a huge number of variables that have a large effect on this, such as the type of lubrication used, the condition of the threads, what washers are used and the surface finish of the mating faces. However the best in my opinion is to use locktite and tighten bolts that are loaded in tension as little as possible. Note that bolts used in shear are a whole different matter, because the shear strength of the hook is affected by the bolt torque...
getting back to the rear hook with it's four M10 bolts, I don't believe 7.2 Tons is enough for snatch recoveries. I believe you need at least grade 8.8 bolts there, because you definately want the rope to be the weakest link in the chain.
And don't be worried about pulling the hook out of the chassis, that's going to take around 30tons of force.
Mag ons ons kenniskry met lekkerkry aanhoukry.