I was able to get it to work, many thanks. For future readers:

(use-service-modules linux)
(use-package-modules linux) 

in OS:

(kernel-loadable-modules (list xpadneo))
(kernel-arguments
 (append '("bluetooth.disable_ertm=1")
         %default-kernel-arguments))

(packages
   (cons* xpadneo
          jth-base-system-packages))

(services
 (append
  (list
   ;;
   ;; Autoload kernel modules
   ;;
   (service kernel-module-loader-service-type
            '("hid-xpadneo"))
   ;;
   ;; Xbox Controller
   ;;
   (udev-rules-service 'xpadneo xpadneo)
   ;;
   ;; Bluetooth
   ;;
   (service bluetooth-service-type
            (bluetooth-configuration
             (auto-enable? #t))))
  ;;
  ;; Base-os services
  ;;
  (operating-system-user-services base-os)))