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Originally from Christchurch, Tatupu, 24, is a former Samoan league representative who made his Super 14 debut for the Force in 2008 against the Lions.
Hill, 21, played for Wellington in last year's provincial competition and was a member of the unbeaten New Zealand under-20 team that won the world title in Wales in 2008.
Both players arrive in Dunedin in June to join the Otago training squad for the ITM Cup.