I think that developing animal husbandry without farming is a definite possibility. It could easily come before farming; however, the likelihood of an intelligent species avoiding the development of farming altogether is not very reasonable. There are quite a few reasons why farming is a likely development for intelligent creatures, even if animal husbandry is satisfying the creatures nourishment needs.
There are many other uses for plants besides food
Plants can be used for a wide variety of purposes other than just food. Spices would likely be discovered and cultivated to flavor the food obtained from the animals. Leaves and husks are often used in modern cooking as containers (banana leaves and corn husks are very common). Outside of food plants provide fibers for textiles, pigment for dies and paints, materials for tools or building, and chemicals for industry and medicine. Plant cultivation also produces food for domesticated animals and allows intelligent creatures to raise them more effectively. The variety of uses that plant life offers are not likely to be covered through animal husbandry alone.
Farming is often more efficient than animal husbandry
These creatures are omnivores, and while they might prefer these creatures that they eat to other food, they also will take the easiest path to survival. Plants grow and produce much faster than animals do. Even the fastest maturing animals take months to grow large enough to be used as food. Plants can produce much more food, often more quickly. Plants also require less resources. Soil, sun, and water are often the only requirements. Animals are less efficient energy wise than plants (see the energy cycle). Also, plants grow and produce using much less space than animals. In the area it would take to grow a cow to maturity, a farmer can likely produce much more corn. Also, it is usually less effort to harvest and cook plants than it is to kill an animal and prepare it for consumption. In nearly every way it is more efficient to produce food through farming than through animal husbandry.
Intelligent creatures are inquisitive and often desire variety
If the efficiency and utility of plants is not enough to inspire their cultivation, intelligent curiosity might be. These creatures would likely desire different tastes and experiences. They would likely see plants sprout and grow and would wonder if they could control it. Regardless of their other motivations, they would probably develop farming for no reason other than it being possible.
That all being said, I do think this situation is possible.
Some ways to prevent the development of farming:
You would need to have some very energy efficient animals for these creatures to raise. Perhaps smaller creatures that can gain energy from the sun? An enormous algea-like fish or lizard seems plausible. Basically make the creatures as easy to domesticate and raise as a plant would be.
Making the animals produce other materials besides food would be another good idea. Perhaps their bones are an excellent building material? Their skins an incredibly useful clothing material? You could have them produce venoms or secretions that are powerful medicines too. Any waste could be used to feed the other animals. Basically this animal (or even better a group of very similar animals with slight but important differences) should be a swiss army knife of usefulness.
I think a good example of what I have in mind is found in slime rancher, a game where creatures called "slimes" provide incredibly useful resources and dominate the surface of an entire planet.
Anyway, I'll reiterate the point:
Is a intelligent society using animal husbandry but not farming reasonable. No. But, with the right amount of thought and creativity this situation could be engineered to happen in your world, which would result in a very cool and interesting alien society indeed.
