That’s odd, I thought systemd worked exactly the same no matter what distro it was included in?
The service file I’ve been using from my post: Getting Syncthing running with a central file server running CentOS 7 minimal setup and windows clients
Allows me to use ps just fine:
[root@sync ~]# ps aux | grep syncthing
ataraxia 680 0.0 0.2 274672 4848 ? Ssl May11 6:24 /usr/local/bin/syncthing
ataraxia 6949 4.1 9.4 1310216 177652 ? Sl May11 1027:27 /usr/local/bin/syncthing
root 29231 0.0 0.0 112644 964 pts/0 S+ 19:27 0:00 grep --color=auto syncthing