Can I play Arma Mobile Ops on more than one mobile device?

Yes, you can. To do so, first check what operating system your devices use and follow the steps below.
 
If your mobile devices use iOS:
1. Open your device settings.
2. Find Game Center and sign in.
3. Open the game and select Settings in the lower right corner of the screen.
4. Connect to Game Center via selecting the option "Disconnected" next to the Game Center symbol.
5. Install the game on your other device and open it.
6. Open your other device settings.
7. Find Game Center and sign in.
8. Play through the tutorial and ignore creating a new player.
9. Select Settings in the lower right corner of the screen.
10. Connect to Game Center via selecting the option "Disconnected" next to the Game Center symbol.
11. A window will appear with the choice to start a new user or use a previous account/player name. Select the previous account/player name.
12. Now the game will be synchronized across your devices.
 
If your mobile devices use Android:
1. Open your device settings.
2. Find Accounts and open it.
3. Choose Google Play and sign in.
4. Open the game and select Settings in the lower right corner of the screen.
5. Connect to Google Play via selecting the option "Disconnected" next to the Google Play symbol.
6. Install the game on your other device and open it.
7. Open your other device settings.
8. Find Accounts and open it.
9. Choose Google Play and sign in.
10. Play through the tutorial and ignore creating a new player.
11. Select Settings in the lower right corner of the screen.
12. Connect to Google Play via selecting the option "Disconnected" next to the Google Play symbol.
13. A window will appear with the choice to start a new user or use a previous account/player name. Select the previous account/player name.
14. Now the game will be synchronized across your devices.
 
If you want to use both iOS and Android devices:
At the moment this option is not available, but it will be added soon.