This is true, but it will glitch your guardian ranks initially. Due to the gross disparity in XP offline vs online, you might grab 20 or more tokens an hour offline, but then as soon as you go back online, the game tries to recalculate and it puts you in a huge token hole. To get your 21st token, you would need to gain 21 levels of online experience, which will take you way longer than what it took offline to get the initial 20. Another thing is that while offline is good for farming legenadies in general, you can't get legendary class mods without the hotfix.
If you do plan on doing this offline, it would be good to hit 224 guardian tokens to reach the capstones of survivability and hunter, and stop at 74 in the other one. Hollow Point is currently bugged and can kill allies. After that, go back online and ignore the tokens until you can actually gain them again.