While testing out the zombie baby villager jockey mechanics which states that it has the ability to ride zombified piglins when attacking players or when it's original ride dies, in observation, the Zombie baby villager jockey doesn't approach or ride the zombified piglin riding a strider, which would originally result in a triple stack 

Steps to duplicate:

1. Summon a baby zombie jockey
2. Kill kill it's original ride, if applicable 
3. Summon an adult strider jockey (Zombified piglin as passenger)

Observation:

The baby zombie villager jockey can't ride or will not ride the zombified piglin riding the strider, in which sources like the minecraft wiki (still not sure if it's valid source) states that Zombified piglin is one of the mobs it can ride