The corals you listed aren't super "clean" water demanding, so it's not an easy answer (well it could be "yes, you always need a skimmer" but I don't like that answer much.)
It goes more to your tank, how comfortable you are with it and being able to see how it's doing. My Max has a skimmer, but for the better part of it's existance has been essentially skimmer-less as the fluctuating water level in the back chamber has prevented the skimmer from functioning very much. If this is a similar situation to yours, I'd recommend learning to run the tank skimmer-less (keeping an eye on nutritients and preventing build up either by limited feeding or removal of waste via water changes or sufficient algae growth in your 'fuge.) If however the water level stays consistent, if your skimmer is functioning quite well, then I'd say leave it and make use of it.
