The brushes used for nail art and for the base coat of nail polish are very different. The base coat just uses the brush in the bottle (acrylic, wide and flat). Nail art uses a variety of different style of brushes depending on what you are painting, but the preferred material is...
(Pauses to allow screaming to stop)
Nail art can be painted in acrylic paint, sealed with clear nail polish, gel polish (UV cured, thins with rubbing alcohol), or nail polish (thinned with nail polish thinner, not acetone). Airbrushing is done with acrylic paint usually. Stamping is done usually with nail polish but there are now a few UV gels for stamping.
This means that I have 4 sets of brushes, and rain the fury of hell on anyone who mixes them up.