It would appear so, but follow these links.............
http://www.tikka.fi/pdf/datatables/TikkaT3Datatable2013.pdf
http://www.tikka.fi/pdf/Tikka_catalogue2002.pdf
On that basis any other T3 twist-rate would be non-standard.
U.S. makes seem to be standard 1:10" with a few in 1:12".
This does make one wonder if a preoccupation with rates of twist matters very much in practice. The only occasion that I've ever seen where this has had an effect is military 5.56mm Nato 62gr - and commercial equivalent designs - fired from standard 1:12" .223 Rem which flew all over the shop. Some shots failed to register even on 4' by 2' target boards at 100M, so only God knows where they went