If a non-Human creature enters the battlefield as a copy of a Human creature, it won't get a +1/+1 counter. Similarly, if a Human enters as a non-Human creature, it will get a +1/+1 counter.

A non-Human creature you control that would enter the battlefield with no +1/+1 counters on it enters with one +1/+1 counter on it.

Any other non-Human creatures that enter the battlefield at the same time as Grumgully won't get a +1/+1 counter.