Can Adobe Photoshop CS6 or Lightroom 4 sold as 'US only' be activated in other countries?

There isn’t a reliable universal rule based on the information provided. Community experience suggests some region-labeled retail copies have activated successfully outside their intended sales region, but the only definite way to know for a specific copy is to try it. Adobe’s activation policies can also change over time, so past success is not a guarantee. In short: the distribution label may not always mean strict activation locking, but you should not assume worldwide activation is guaranteed.