No, they don't get cramps. Yes, you CAN have them spayed while they are in estrus, but it is a more risky procedure and most vets will want to wait until she is out of estrus unless you have a really compelling reason to have it done rightfuckingnow.
As an aside, when she is "spotting", she is actually in proestrus, the stage before she is fertile. Once she STOPS spotting, she will be fertile for up to two weeks, and will attract dogs from miles away. Sperm can live in the reproductive tract for days, so I heartily recommend keeping her in the house (not the yard unless you are there) for the next three weeks or so.
Trust me, some dogs can do amazing things to get to a bitch in estrus and the number of owners who only keep their bitch indoors until they stop bleeding astounds me. >.<
As an aside, when she is "spotting", she is actually in proestrus, the stage before she is fertile. Once she STOPS spotting, she will be fertile for up to two weeks, and will attract dogs from miles away. Sperm can live in the reproductive tract for days, so I heartily recommend keeping her in the house (not the yard unless you are there) for the next three weeks or so.
Trust me, some dogs can do amazing things to get to a bitch in estrus and the number of owners who only keep their bitch indoors until they stop bleeding astounds me. >.<