function PointSource (args){
  ol.source.Vector.call(this, args);
  this.typeOfGeometry = 'Point';
  this.on('addfeature', function(e){
    if(e.feature.getGeometry() instanceof ol.geom.Point)
      console.log('point');
    else {
      console.log('no point');
      this.removeFeature(e.feature);
    }
  });
}

PointSource.prototype = Object.create(ol.source.Vector.prototype);
PointSource.prototype.constructor = PointSource;

var myPointsLayer = new ol.layer.Vector({
  source : new PointSource({...})
});