Generally, when a downloaded resource pack is missing a texture for a certain thing, it is replaced by the default texture. When I downloaded a resource pack that didn't have a texture for the attack indicators, the attack indicators didn't show up at all. Due to past experiences, the indicators should show up with the default texture. This may be happening because it is a new texture piece in 1.9. I hope this can be fixed soon, because the indicators are very important for PVP.