As no-one else has answered this I will try to but if anyone knows more or if I am horribly wrong, please jump in.
Modern Universal LNB's use horizontal and vertical polarisation which is controlled by a voltage set by the receiver and detected by the LNB. Rotational polarisation is a system that allows the receiver to control the amount of polarisation applied so as to maximise the signal.
So the answer is yes you would need a special receiver and LNB.
You don't need a special receiver to get circular polarised signals. Although to receive circular polarised signals with a linear polariser you need to fit a dielectric slab at 45 degrees in the throat of the waveguide. However, you will need a dish size of 250cm for Sirius in the UK and 150cm for Thor 1. Indeed, if the signal strength is sufficient you will be able to receive such with a linear LNB although the signal will be attenuated by about 3db.