My periods are pretty irregular to begin with. Usually I avoid intercourse on the first day or two when the flow is heaviest. After that we go for it if we are so inclined. Personally I do not see a problem with it as long as he is OK. If he is uptight about the bit of blood, he can always wear a condom. He should anyway unless you are on birth control or not concerned about getting pregnant.

If you are only going for manual stimulation, wearing a tampon is a good idea. There are other ways to bring him off, if needed too. ie. oral, etc
More important is to be in a loving relationship, preferably your spouse, Then what ever the two of you agree on is ok