It's not like you're asking money for it. That would be the only reason I would ever have an issue with someone incorporating something I've made in a mod. As long as you give credit I doubt you'd ever receive any blowback. Especially with big game studios it's better to ask for forgiveness than permission. The worst they would do is send you a cease and desist but that would undoubtedly snowball into a "Streisand effect" just like the OuiOui and Prostock Drag Mod for NR2003 back in the day.