There's a number of DAPs that don't make use of ReplayGain tags. Cowon, Philips and Sony players don't. Some sandisk players have a setting for using with RG tags but they seem to be inconsistent with how they handle them. iPods can use Soundcheck but from what I've read it's a setting that has to be activated through iTunes. I've also come across a number of android music apps that don't use ReplayGain tags.
Instead of trying to keep track of which DAP or didn't use RG info from tags I decided to just start applying the ReplayGain to the files themselves as part of my transfer routine. I usually use MP3 files on all of them and it only takes a few seconds.