ernestnywang's point could also explain the reluctance of some carriers to give other airline elites access to contract lounges- we had a thread about MH@PNH denying a while back..

(In Y, I was however given access to contract lounges by MH in DEL and HKT. UL went a step further and proactively asked if I had any guests, when checking in @ SIN..and the Lounge Invite read something along the lines 'Due to CX DM card/OW Emerald'..UL's bp/invites actually state Cathay Diamond along with emerald)