Jackson and Ortiz were stablemates under Oyama at the time weren’t they? Still, I don’t recall ever hearing a story of how they fared with each other in sparing...
Anyway, Ortiz would have still had his way with Silva, in my opinion, but Arona, Noguiera, Rua, even Nakamura would have probably bested him.
The grapplers in Pride were on another level than the ones he fought in the UFC. Matyushenko was probably the best grappler Ortiz had to fight during his resurgence after Frank Shamrock, and Matyushenko was completely drained from the weight cut coming into that fight. Ortiz would not have been able to simply hold down the guys Pride had to offer.