It is not mandatory for a Mercalan to be a Solmancer or a specific race, as they are supposed to hold no prejudice, what is required at it's most basic is to follow the tenants rigorously. Mercalans are also not always Curates in the end, they can be simple doctors and paramedics. It is said that the simplest prayer to Mercala helps greatly on any healing procedure, of course, if your intent is to help the others.
The ultimate goal of the Mercalan Church in regards to healing magic is to make sure mankind don't develop a dependency on it, so one Mercalan should always weight the specific case against that to determine their answer to when or not use any healing magic.
Most tend to be pacifists, or at least soft on injuring enemies, because it is the most effective way to solve conflicts (In case of a bandit, for example, you'd know why they're doing that, and probably help them repent, killing them wouldn't had helped, etc.) and at the same time, they won't need to waste their healing magic with something that could be easily avoided.