yup. they are safe. just like a 1911 chambered and safety on is safe.If it is true that a holstered Glock with one in the chamber is safe, then it surely follows that another holstered handgun with one in the chamber and thumb safety engaged is, at a bare bones minimum, at least as safe.
but, I won't carry a 1911 concealed because again, I don't like how easy it is to flick the safety off and pull that very light, single action trigger.
just personal preference. I love my 1911 that I have tricked out for competition shooting, but I'd never carry it.
then again, with the modifications to the safeties and trigger, Ive forgotten how a "bone stock mil-spec" 1911 feels, so maybe if I went and bought a second 1911 and left it alone, I might feel safe carrying it. however, I prefer my Beretta again, because I can carry 15+1 of .40 and the mag sits flush with the frame, instead of 10+1 of .45 if I'm using my extended 1911 mags.
(and some folks will prefer to carry 9mm because they can carry 18+1 capacity in the same size package)