Air Contractors have been operating on behalf of DHL for as long back as I can remember. At various times they've been rumoured to replace EAT, and it wasn't long after DHK had sprung rumours started floating they'd replace them too.
DHL has always had a policy of having a mixed bag of owned and not-owned airlines operating for them. They are also not afraid to move metal around, and I don't think DHK had to search very hard to crew the 757 they had based in SYD (or was it AKL?) for a year or so. Neither did EAT find it difficult to crew A300s flying into places hot, sandy and unwelcoming from BAH, even after the bad guys got lucky.
A third party carrier is not there to 'steal' jobs of wholly owned DHL airlines (of which there are quite a few). Either it's because of traffic rights, geography or for growth and to keep e.g. DHK bosses sharp in the competition to grab some of that. That's the mechanism which landed the 767s with DHK years back, in sharp competition with EAT, '3rd party' and ABX from across the pond.