Yep, for PowerSteering fluid, just use the same MerconV that should be in your 5r55e Transmission.
No sense in buying an overpriced seperate bottle labeled "Power Steering Fluid".
Keep a tight lid on the bottles & moisture intrusion should not be an issue, unless you live in CentralAmerica.
Every 6mths, got a routine of HandPumping the PS reservoir empty then refill with fresh MerconV;
also HandPump 2qts of old fluid from the TrannyDipStickTube & refill with 2qts of fresh MerconV,
along with the usual semi-annual EngineOil+Filter change.