Depends on the contract. If the client engages a single contractor then regardless of how many subbies the contractor brings it is a single set of RAMS covering all works provided by the firm taking the clients money. Where the sub-contractors are also directly engaged by the client e.g. due to specialist work the main contractor could not cover then the sub-contractors RAMS would be required. Communication wise as contractor I would expect to see a subbies RAMS so as to review their plan against ours to make sure we were all working in the manner notified to and agreed with the client.

Sub-contractors should have their own RAMS. That said, it is sometimes the case sub-contractors work under the RAMS of the main or principal contractor. Ultimately the PC is responsible for site safety and it's their choice how sub-contractors are engaged and managed, unless there is anything in the T&Cs of the contract which states otherwise.