It should be compatible with both.

But for Gauntlet's Race Mod you have to remove a few file as indicated in the readme:

You need to delete the following files:
GRM\Game\AbilityDefs.xml
GRM\Game\GalCiv3GlobalDefs.xml

You need to delete the folder:
GRM-Commanders

Will you be updating this one to the latest release? (when I loaded it up, the game wouldn't load) and I really liked this mod.

Looking at the files, the mod is mostly compatible with GRM. There are a few conflicts but they are pretty minor.

1) Commander abilities/blueprints. Remove GRM-Commanders from your mod folders for compatibility. Failure to do so won't crash anything, but it will be random which set of commander modifications will take precedence.

2) Various event files. You could remove GRM-Ideology and GRM-Ideology for Intrigue to ensure compatibility. Leaving them in shouldn't crash anything and again, it will be random which set takes precedence I believe. I recommend leaving these GRM components in as they also modify other content you may want.

3) This mod is modifying GalCiv3GlobalDefs.xml... my most RECENT versions of GRM no longer mod this and hence are compatible, but if you are using a old version you will have to remove this file from GRM... which is only used to modify racial ability choices from 2 to 4. So be prepared for that... again... if you are using an old version of GRM.

PS: GRM no longer modifies abilitydefs either... so you don't need to delete that unless you are using a old version of GRM.

Be careful too, because I updated for Crusade when retribution released, for version 3.5 Hotfix/OptIn and that will likely be the last update for non-retribution.