I highly doubt that RTV would hold up to the shear that that rubber-metal contact area is subjected to. As you can see in the cutaway diagram below, all of the power/torque to the final drive is transmitted via that rubber insert from the front half of the drive shaft to the rear half.
What he said.
The rubber is probably vulcanized in place in the driveshaft and is intended to absorb torque shock from the inconsistent rotational speed of the shaft due to the universal joint(it's why the axles of front wheel drive vehicles use constant velocity joints). The amount of torque and the rotational speed changes will break whatever adhesive you try to bond it with.
Having said that, one of the strongest adhesives that I know of is 3M 5200 urethane adhesive. I have seen sailboat keels weighing well over 2 tons held firmly in place by a contact patch of less than 1 square foot of 5200 adhesive. Anyone who has attempted to break the bond this stuff makes will attest to it's strength. One of it's features is that besides being unbelievably strong, it is also flexible which can be useful.
You could give it a try, just make sure that the surfaces to be bonded are spotlessly clean and follow the directions. Get it at Home Depot or a marine store as it is mainly used in boat construction and repair. It's not terribly expensive, about $20 for a tube with enough to do your drive shaft.
https://www.3m.com/3M/en_US/p/d/b40066983/One word of caution, NEVER use it on anything you might ever want to take apart.
