If you keep it as a Chansey, you can put it in gyms that already have a Blissey.
I was reading somewhere, didn't bookmark unfortunately, someone was commenting that because the main point of Blissey/Chansey is to take up as much of the attacker's time as possible, and because losing HP gains energy ... the ideal Blissey/Chansey IVs for stalling might actually be 0a/15d/15s so that you deal less damage to the attacker and don't help charge their energy.
