The link you posted is for transmission running inside a VPN. I am not sure about jackett - don't know what this is. Sorry.
I use the haugene docker with PIA as the VPN provider. Works great. Below is my compose file (with a few bits redacted of course) 
First you need to install and configure the compose plugin for OMV 6/7. There is loads of info on this in the forums so I am not covering it here.
version: '3.3'
services:
transovpn:
image: haugene/transmission-openvpn:latest
container_name: transovpn-pia
cap_add:
- NET_ADMIN
restart: unless-stopped
security_opt:
- seccomp:unconfined
logging:
driver: json-file
options:
max-size: 10m
ports:
- 9091:9091
dns:
- 8.8.8.8
- 8.8.4.4
volumes:
- /etc/localtime:/etc/localtime:ro
- /symlinks/omv-system/appdata/transovpn-pia/data:/data
- /symlinks/omv-system/appdata/transovpn-pia/config:/config
environment:
- OPENVPN_PROVIDER=PIA
- OPENVPN_USERNAME=xxxx
- OPENVPN_PASSWORD=xxxx
- LOCAL_NETWORK=192.168.1.0/24
- OPENVPN_OPTS=--inactive 3600 --ping 10 --ping-exit 60
- PUID=${PUID}
- PGID=${PGID}
- TZ=${TZ}Sie haben noch kein Benutzerkonto auf unserer Seite? Registrieren Sie sich kostenlos und nehmen Sie an unserer Community teil!