First off, what the rogue is doing may be unnecessary, as all he needs to do to satisfy the conditions for a Sneak Attack is to have an ally within 5 feet of the target. Having advantage on the attack (e.g. from being unseen) is only one way to generate a Sneak Attack on a target.
Secondly, the Rogue is not able to hide behind a PC, due to the rules on hiding:
You can’t hide from a creature that can see you, and if you make noise
(such as shouting a warning or knocking over a vase), you give away
Once the Rogue is spotted by a creature, he cannot hide from the creature unless he breaks line of sight.
Ducking behind a character does not count as breaking line of sight. It only provides half cover:
A target with half cover has a +2 bonus to AC and Dexterity saving
throws. A target has half cover if an obstacle blocks at least half of
its body. The obstacle might be a low wall, a large piece of
furniture, a narrow tree trunk, or a creature, whether that creature
is an enemy or a friend.
There's one exception to this: Lightfoot Halflings can hide behind other characters due to their Naturally Stealthy racial trait:
You can attempt to hide even when you are obscured only by a creature
that is at least one size larger than you.
But remember: this doesn't exempt them from the observation rule.
The best bet for the Rogue character is to wait until one of his allies is within 5 feet of his target before launching a Sneak Attack.
Thirdly, the Cunning Action feature lets rogues Hide as a bonus action, not a free action. A minor point, but its use precludes the use of any other ability that can be used with a bonus action (like a second weapon attack with Two-Weapon Fighting).
As a final note, frequent Sneak Attacks are expected to occur often with the Rogue. This may seem overpowering compared to the fighter. However, the Rogue has a single devastating attack, while a fighter is able to generate multiple attacks.