In any movie production, the better the actor, the better the film. If the regular actor can perform the role better than one who is an actual dwarf, why not.
If we look at many of the best selling films, we have actors portraying people they are not. Roles like people with cancer, people who are mentally disabled, and so on. For the most part, the only way an actor/actress would not be doing a role they are not is if they played themselves.
Are there dwarf actors? Yes, but just having dwarfism does not mean you can perform the roll. If fitting the description of a character was all that is needed, anyone could be an actor.
There is also the issue of the dwarf meaning. You see, in many films, dwarf is a race of people like in the movie Lord of the Rings, as compared to people with dwarfism, a physical condition.
Hey, if you don't like that actors are playing people that they are not, by all means, stick to reality TV where people are supposedly playing themselves.
Yes, it is okay for a regular actor to play a character with dwarfism in a movie. If the actor does a good job, the part will be believable. Actors play a wide variety of roles that do not typically fit their actual persona as part of acting. Playing a character with dwarfism should be viewed no differently.
Actors famously spend lots of time "resting" or waiting tables between jobs, but people of restricted growth can find difficulty getting ordinary work due to accessibility problems or prejudice. Where do we draw the line? There are many excellent little people actors as Bob Hoskins, Ray Winstone, Nick Frost and Toby Jones.
It is ridiculous and condescending that regular actors would portray someone with dwarfism in a movie. There are several actors and actresses with the condition who are actually very good at their craft, so there is no reason to get someone else to play them. Would people want a dwarf actor playing Michael Jordan?
While there are props, belts, and computer generated ways to make anyone any size, there are a large number of people who are dwarfs in the Screen Actors Guild. Taking away someone's job, someone who is just as talented, just not as tall, is wrong. There are more regular parts than those for dwarfs.