Allen and Dacey both slot into the starting line-up as Head Coach Danny Wilson makes three changes to his team that defeated Edinburgh Rugby last time out for the big clash in Italy.
Wales Under-20 star Jarrod Evans is retained by the region for the game and selected at fly half, with Rhys Patchell switching to full back and Dan Fish moving to the wing.
Italian international Number Eight Manoa Vosawai is named in the back row and will face his former club.
Prop Taufa’ao Filise, lock Lou Reed and centre Garyn Smith are all recalled to the replacements bench.
Head Coach Danny Wilson said: “We’ve hit some good form in the Guinness PRO12 in recent weeks as we look to move up the table, but we’re well aware of the challenge we will face in Italy against a Treviso team who will be fired-up to claim a victory.
“We only need to look at our away game at Zebre earlier this season to fully understand that our attitude, preparation and performance must be right if we want to come away with the right result.
“It’s good to see Cory Allen and Kristian Dacey back in the set-up, after they were released by Wales, and we look forward to seeing them both put in big displays for us in Italy”
Cardiff Blues: 15 Rhys Patchell, 14 Blaine Scully, 13 Cory Allen, 12 Rey Lee-Lo, 11 Dan Fish, 10 Jarrod Evans, 9 Tavis Knoyle; 1 Thomas Davies, 2 Kristian Dacey, 3 Salesi Ma’afu, 4 Jarrad Hoeata, 5 James Down, 6 Josh Navidi , 7 Ellis Jenkins (c), 8 Manoa Vosawai
Replacements: 16 Ethan Lewis, 17 Bradley Thyer, 18 Taufa’ao Filise, 19 Lou Reed, 20 Macauley Cook, 21 Tomos Williams, 22 Garyn Smith, 23 Aled Summerhill