Yes you can put 28mm on a hybrid rim.
The conti TT is probably best in its 32mm incarnation.
The 28 is a bit thick for a fast tyre, and for a rugged tyre, its better to go slightly thicker than 28, but if youve already bought them, they will work.

Some 28mm are a bit thin and fragile. Panarcer Pasela is popular with endurance riders, but is very narrow. I find the 32mm is about the size a 28mm tyre should really be.

Running 28mm tyres will make your bike faster, but they are generally rugged enough for city streets and even some off-road trails. Its not a common size to use, which is a shame, since it the best all-purpose tyre size you can get.