What size hot tap are you looking to perform on the 6" Pipe? While angle taps are not routine, you can contact several experienced contractors for this sort of service.
Here is a press release from Furmanite concerning an angle hot tap. They have offices around world that perform this...
What kind of system are you looking to install the fitting onto? If it is a cross country pipeline, you can only install bolted mechanical hot tap fittings as a temporary connection and they have to be seal welded at some point in the future. This is a DOT requirement. If you are in a plant...
I didn't see anywhere where the size of the Hot Tap was adressed. There is a pretty large difference between performing a full size 18" Hot Tap on the existing 18" Pipe versus a smaller Hot Tap, such as a 4". If you are making a small branch connection, the weldolet should be a safe bet. If...