The RV industry seems to use the terms EMS & Surge Protector to often describe the same device, or a bunch of different devices. Technically, a surge protector
only does one thing - it absorbs the energy of short over voltages (spikes or surges). They are often sold for homes in lightning prone areas, added to plugging strips, etc. They are rated in joules - poorly designed ones not capable of absorbing a useful amount of energy are often added to plugging strips and other devices as a sales tool.
True EMS devices usually have surge protection built into them (although sometimes not enough) as well as other functions. In larger RVs, some Energy Management Systems also detect whether the RV is plugged into a 50 amp or 30 amp pedestal, and can "shed" or disconnect loads to prevent overloading the pedestal breaker. The best of these allow the owner to choose the load shedding order, for example, if the microwave starts, the AC shuts off, or provides automatic switching between two air conditioners.
On top of all that, there are also "Autoformers", devices that automatically raise low campground voltage to prevent damage to air conditioners and other motor driven devices due to low voltages. Because they often have EMS functions as well as the voltage adjustment capability, they are also sometimes called surge protectors or EMS.
You really need to examine the specifications of the device to be sure it is going to do what you expect. Like Jim, I installed the built in version of the Progressive Industries EMS HW30 in my trailer - it has shut down the power to my trailer a couple of times for low voltage & once for reversed polarity.