Dragons trailed 10-7 at the time of the dismissal, but fought back to share the spoils with Benetton after a last-minute try by wing Fine Inisi, with Angus O’Brien’s conversion from the left touchline going wide.
Tiatia’s side have a URC double-header against Stormers and Lions in South Africa after the Six Nations before a trip to Stade Francais in the last 16 of the Challenge Cup on 5 April.
Well-travelled Douglas has proved to be a big hit since arriving at Rodney Parade from Biarritz last summer.
The powerful lock has played in 13 of 16 games, with eight of his appearances as a starter.
Dragons will welcome Ben Carter back from Wales duty and also have Seb Davies, Matthew Screech and Barny Langton-Cryer as options at lock.
Versatile forwards Ryan Woodman and Shane Lewis-Hughes have also previously slotted into the second row.
