There is no regulation that requires the paying of any money into an NPF entity, other than a mess, unless it is for a voluntary activity (e.g. in order to participate in a base club).
Even the issue of mess dues is often misunderstood. The only NPF regulatory requirement with respect to messes is that every CF member must belong to one. Over the years, however, I have seen folks claim that this means one has to pay mess dues. This is not entirely true. There is no regulation that requires the payment of mess dues. However, before everyone does a little happy dance and marches off to cancel the allotments to their messes, further explanation is required. There is no requirement to pay mess dues per se, but there is still that requirement to belong to a mess. With that comes a requirement that the mess remains solvent. If solvency requires the payment of mess dues by the membership, then mess dues are legally authorized and required. There was a case a number of years ago where a raise in mess dues was twice voted down by the membership and so the base commander imposed the raise. The legal ruling was that since the Base Commander had a legal requirement to ensure solvency in the messes, he also had the legal authority to raise mess dues as required. It's worth noting that this was not done on a whim, the situation was well researched and the raise involved was approximately $1 per month.
The requirement to belong to messes and the fact that membership may involve mandatory mess dues has been legally tested and so I don't want to get into that.
The trouble is that every once in awhile, some folks get some pretty silly ideas into their heads. For example, there is the case of COs of HMC Ships. They don't pay mess dues. This is not a special privilege of the captains of ships. It is simply because by regulation and tradition, COs of HMC Ships "mess alone." That is, they belong to a mess with a membership of one individual. I suppose he could charge himself mess dues if he wanted, but I'm not sure what the point of that would be and I would also be concerned about a CO who did charge himself mess dues. Would he also conduct mess meetings with the voices in his head? Another example saw an attempt by a base mess to continue charging mess dues to individuals posted to certain overseas missions. The argument was that because these individuals would not be paying mess dues overseas, then they "had" to pay mess dues at home because mess dues are a requirement. Again, this is not the case. Every member of the CF must belong to a mess and if that mess charges mess dues, then every member must pay them. However, it is up to the mess whether mess dues are charge and at what rate (i.e. that required to maintains solvency). If a mess charges $0, that is perfectly OK. There is also a maximum rate based on a percentage of pay, but cases where that maximum is reached are extremely rare.
In response to the OP's question, has a mess been properly established and constituted? If not, there is no justification for mandatory payments into an "RSM's Fund." It is indeed possible that a combined mess has been authorized. Remote units often do have combined messes and this could be the situation here. However, if this is the case, there should be some paperwork to back it up. Specifically, the CO of the unit that is responsible to provide messes (usually the Base Commander responsible for support services as per the CFOO) to the unit involved should have authorized the establishment of the remote combined mess in writing.
One way to subtly test whether everything is on the up and up is to request a receipt for each payment. If you're paying by cash or cheque, then you should receive a CF 602 (NSN 7530-21-907-5906) for every payment. This is an accountable document that only a properly constituted NPF entity is allowed to have and issue. So at least if they are issuing those, then you can tell that the money is actually being properly accounted for. It should also mean that your money is then being deposited into the Central NPF bank account (a regulatory requirement). If these things are not happening, then the "fund" is not authorized and has no more legal basis than the office coffee boat (i.e. strictly voluntary). Now, the fact that the money is properly accounted for (i.e. Central NPF Bank Account, CF 602s, etc) does NOT mean that the unit necessarily has the authority to make payments mandatory, but it should settle the question of accountability.
Unfortunately, I'm not sure if new DAODs have been drafted, but the references for this used to be CFAO 27-1 and the non-public funds manual (used to be referred to as CFP 105)