Now that Vit and Str scale equally with AP for tanks, there is no good reason a tank, either MT or OT, should be taking Str accessories. The marginal DPS increase you might hypothetically get from it is not worth the sacrificed HP, and as others have said on other threads, it is fully possible to have a full Fending set now with zero Parry (if you really want to avoid it that much, which might be advisable in the OT slot). In general, the concensus for these pieces is to slot Str materia into them, but that's mainly because they can't get any more Vit. You'll also want to be conscious of your Accuracy, since OT doesn't benefit from the tank stance Accuracy buff.
Also, DRK does have OT utility. In the absence of a MNK, they bring the Intellect debuff, and are one of the more capable tanks at grabbing adds. However, a group will benefit more from having the DRK in the MT slot, since they have the highest theoretical MT DPS of any of the tanks, and bring more utility that way (not to mention, DA+DM can counter some of the tankbusters in A8 better than any other tank can).