Red Bull drivers, of witch Carlos came into F1 as, are encouraged to get one other sponsor to come with them. You could say that Max is a pay driver as he has Jumbo as his sponsor, Alex has brought Moose to Red Bull and Toro Rosso. Gasly and Daniel dont have a personal sponsor as far as i know. Some drivers dont have them, some do, its personal choice with them.
You could say Carlos was a pay driver, however that €8m that comes with is a bonus, have a look at what that has got them across STR, Renault and McLaren, STR had a large EG exposure, Renault had it just at the head rests, McLaren has been their best value as they have the rear wing end plate and headrests. The rate cards are very different.
EG may be on the Ferrari, however EG will have top pay Phillip Morris as they are Ferraris ad broker. They will probably give them a small exposure as Shell, UPS and Ray Ban all pay in excess of €25m for their element of the sidepods. €8m wont go too far, maybe a small logo on the headrest area, or on the wing mirror housings.