I've fed beet pulp in the past. If you buy the shredded beet pulp, there is no need to soak it first. People used to think that if a horse ate dry beet pulp, it would expand in the horse's stomach and cause colic/death/etc. This isn't entirely true, and it depends on how much beet pulp you are feeding. But, just to be on the safe side, I only ever fed shredded beet pulp, and not very much (one typical feed scoop in the morning, and one at night). Back in the day, we'd soak the beet pulp in a giant bucket and keep adding water until it was mush. My skinny TB would eat it wet, but it made such a mess and was always full of flies and bugs - blecch!
I was feeding it to my elderly horse because he was looking ribby and he wouldn't eat large amounts of hay. It did put the weight on very quickly, but he lost interest in the taste just as quickly.
What I'm feeding now is a mixture of Ultium (simply because my gelding likes the taste - it's a high performance feed, which he doesn't need but my other horse needs that level of nutrition) and stablized rice bran pellets. The rice bran pellets do the same thing as beet pulp, but are much safer with regard to choking, etc. The horses seem to like them too - I've never had a horse that refuses to eat them.
Stephanie is right re: sugar content. My friend's horse was insulin resistant (pre-Cushings) and she was getting beet pulp before she was diagnosed as IR. She ended up foundering before my friend's vet made the diagnosis.
Why would you be feeding beet pulp? To put on weight? To replace the amount of hay fed? There are a variety of situations where horses get beet pulp - one barn I was at fed all the horses beet pulp, whether the owners liked it or not.