With respect to Neptune, some non-Neptune gear you can control through IOTA or the MXM module - but most of the time it will simply be toggling the power outlet on/off.
Hydros is compatible with other equipment. Is there specific ones that you would want to use with it? I use a Kamoer KH Carer with mine for alkalinity testing. I also control my EcoTech MP10's with a wave engine but the newer EcoTech MP series pumps cannot have their firmware downgraded to pre Mobius and the RF modules that are compatible are harder to get and you would need one of those. There are several other wave pumps that do work with the wave engine though.