I was told that my husband shouldn't hold our newborn while he's taking Adderall. Is there any truth in this?

Why would they tell you that? If he is not having problems and so long as he has been on the drug to make sure of any side effects then I dont see any reasons why he shouldnt.

Adderall Side Effects | Symptoms, Hazardous Side Effects (http://sideeffectsbase.com/adderall-side-effects/)

In reading the details in cdad's link, if he has certain symptoms or side effects among those listed, maybe it is very possibly good advice you have received.
Ask his Dr. if you should be concerned (if that is possible).

If he's not showing any symptoms or doing anything wrong, I'd say that's a pretty crappy thing to not let him hold his baby just because someone told you this.

Odin is correct. The "who said it" is the key.

Yes, I agree ! Maybe the MIL

The person who who told you this needs to be taken out back for some "education". Because they sound aweful spiteful.

Dumb advice.