As a business owner and a diver I see both sides of this. On the business side, from the resorts point of view... Mom and Pop dive ops are making their livings by picking clients up at a pier paid for by the resort and yet they are all up in arms when the owner of that property expects a small fee for the use of it. Meanwhile, if I want to rent a BC from such a dive op, they will charge me 4 times as much as the dock fee per day. The pier cost roughly four times what that boat, motor and all the scuba gear in it are worth and yet the fee to use it is less than the tip to the DM for one tank of diving. Seems very reasonable to me, especially since you are not only using their pier...but you are a competitor to their onsite dive op. Assuming of course that that fee is still the few bucks it was when this was discussed a few months ago.
The sense of entitlement that some dive ops show in which they appear to sincerely believe that they have the right to use a pier that they didn't pay for, don't maintain and if a hurricane destroys it will not help to rebuild amazes me. You don't own it. Simply tell your clients to take a taxi to your pier (if you own one). I would take a taxi to Aldora's pier without hesitation if they asked me to do so.
I got a massage at my resort on our last trip after some blue water motoring for a spear fishing trip trashed my back...the hotel charges the massage company 30% of the massage fee. You know what I call that? The price of doing business.
As a diver...no, I don't want to pay to use a pier. I pay a dive op for that. They are making money from me, by picking me up on that pier. So increase your cost by $3 a day for those staying at the places that charge these fees and stop being so dramatic about it. You don't own the pier. Just like I don't own your boat...and I won't complain and ask for an email campaign if you want to charge me for the use of it.
I've stayed at Iberostar. While there I dove with Dressel and Blue XT Sea. Each had it's benefits. The Dressel boat had many more people in it, but it was a nicer boat, the DM was a fun guy, the Nitrox was free and I enjoyed the dives. I would dive with them again......if Aldora's fleet was completely destroyed in a Hurricane and Memo couldn't find a row boat for me to row us out to the reef in.

Would I choose several other ops over Dressel? Well yeah....
Point being...Dressel isn't as bad as they are being made out to be here and a resort who builds a 6 figure (american dollars) pier, maintains it and replaces it in the event it is destroyed.....can charge whatever they want to whomever they want. They own it. If you don't wish to use it, then don't use it but asserting your rights to make money by using their property for free....come on, seriously? It's just silly.
Yes, the client paid for the use of the resort...but they didn't pay for YOUR use of the pier....to make a living from....in competition with the resort.
I find it highly unlikely that anyone staying at a place like Iberostar is going to change those reservations based on $3 a day that their two boat dive op can't afford. The standard tip for two tanks is more than triple that. Iberostar isn't exactly inexpensive, so that fee will likely just be paid by the client and forgotten about or they will change dive ops to someone a bit less dramatic and a bit more business minded who just rolls the cost into their overhead and adjusts their fees accordingly. That dive op change, or the worry that it could happen is more than likely what the real worry is here.
Just my 2 pesos...worth what you paid for it.