Miller, 20, signed for Hull last month but has been unable to train or play for the Black and Whites because he had not yet recieved a visa.
And Ellis, who played with Miller at former club Wests Tigers, is excited for the arrival of the half-back.
He said: “You only have to look at Michael Dobson, Blake Green or even our Daniel Holdsworth, players who never really cemented a position in the NRL but have come here and been a big success. Jacob can do just that and this is a great opportunity for him.
“Jacob is a young lad who has had all the rep honours a young lad can have.
He was signed to be the Wests’ next number seven, but it is a tough nut to crack, the NRL.
“To come in and dominate in that team was always going to be difficult. He’s a great kid though and he will fit in really well with our group. That’s important.
“I was hoping he’d make the number seven jersey his own at Wests, he hasn’t, and that’s now Hull FC‘s gain.”
Ellis played under current Hull coach Peter Gentle at Wests when a young Miller was fast-tracked through the youth system.