Fresh manure of any kind around the plants is not a good idea as the heat and ammonia can damage the foliage. But tomatoes are 'gross feeders' and can easily be given very strong liquid manures.
It is important you only start feeding once fruit has set or otherwise you will get lots of green foliage and few fruit, but soaking horse manure in a bag in a large tub of water would be a good way to make a liquid feed. You could dilute it about five or ten to one with water to be on the safe side.
Having said that, tomatoes need potassium not just nitrogen to encourage fruit and flowering, so a feed which contains more potassium is a good idea. One of the best of these is made from either comfrey leaves soaked in water or failing that, nettles. This makes a disgusting, smelly 'brew' but it is wonderful for tomatoes and every bit as good as proprietary feeds which cost a lot.

But if you mean actual horse manure, not manure 'tea' so to speak, so long as the horse manure has been well composted, preferably with straw for a minimum of a year, rhubarb appreciates a top dressing with it, and the soil generally round other plants will be improved if its added - roses, for instance.