About 50/50. Some teams have helicopters eg. Prodrive currently leasing an AS350B2 having sold their B3 and not yet taken delivery of their EC135T2. They often lease a second one in too for this event. Malcolm Wilson has the Koala too (reg rather appropriately I-RALY....). Then there are drivers who have their own, like Marcus Dodd with his MD600, Colin McRae with his EC120 and his brother an R44. Some of them have jets too - McRae and Prodrove both have CitationJets, Dodd has a Piper Meridian.
There were approx 25 different helicopters used last year, from what I could work out, plus at least three fixed wings for radio relay work between the cars and their team bases.
When the events are outside Europe, then it's a matter of leasing in, but certainly the ones outlined above seem to go all over Europe