reckoners arena procs 2 times hunt from voracious gromp?

Yes — Voracious Gromp has Hunt 3, so holding at Reckoner's Arena gains you 6 XP total.

The Hold half of Hunt triggers naturally on your Hold action (3 XP), and Reckoner's Arena's "when you hold here, activate the conquer effects of units here" forces the Conquer half of the same Hunt keyword to trigger as a separate chain item (another 3 XP). Both resolve and sum (Rule 823.1.b; FAQ #9544). Note the Arena ability only sees the units' conquer effects — it doesn't create an actual conquer, so nothing else like scoring or a real Conquer condition fires.