I think vibrators in general are likely to be fine to use during pregnancy, as long as it is not a high risk pregnancy. I believe the concern is that orgasms can potentially trigger labor. Obstetricians will often suggest couples have sex to try and trigger labor if a baby is past due. The warning, which I think most if not all vibrators carry, is an attempt by manufacturers to CYA themselves in case someone tries to blame them for premature labor or a miscarriage. I can't think of any particular reason why a vibrator would otherwise be dangerous. However, I would think a concerned person should have an honest discussion with their doctor to be sure.

In terms of other toys that may be unsafe to use during pregnancy, I would certainly think electro-stim would be dangerous and ill advised.

I would say they are safe unless the doctor says so. I would think, if one could have normal sex, a vibrator being used in reason should be no problem. I guess, when in doubt-ask the doc.