Hi Mike!
There have been folks who've made damascus out of these two alloys, but I don't recommend it. When you make damascus, there's much more to it than just putting two different steels together. You really need to be aware of the compatibility of the two steels. By that I mean taking note of the expansion/contraction coeffiecents of each steel. (How much each of the steels expands/conctracts when heated or cooled.) as well as the composition of each steel, and how each reacts to the other, and to heat treating. In this case (5160 and O-1) you would likely have an easy enough time welding them, but the problems would occur in drawing them out, and in the heat treatment. It's very possible that if you joined these two alloys, they would likely tear themselves apart during hardening/quenching. 5160 will contract more than O-1 when quenched. The trick with damascus is to find two steels that are somewhat similar in their makeup, which means they will react similarly when heated/cooled/hardened/tempered, in order to experience the least amount of problems.
I know that properly forged and heat treated 5160 will out perform A-2. With O-1, in order to achieve the same type of hardness as A-2, it's going to be somewhat brittle.
Any time you try to make blades, it turns into a compromise. Keeping in mind that there are only a couple of steels that were ever actually designed specifically for knife blades, we, as the Bladesmiths have to determine the characteristics that we deem the most important in our blades. Then we have to choose the steel(s) that will allow us to get as close as possilbe to those desired characteristics. Most of the time we wind up giving up something to get something we want. For example, over the years I have come to despise stainless type steels. They are extremely difficult to forge, there is just no way to get around the brittlness issue with them, and they are very difficult for most customers to resharpen. This is due to the high levels of chromium, Moly, and/or Vanadium that most stainless type steels contain.
By choosing to use simpler steels I give up the stain resistance, but I'm able to achieve the things that important to my customers and I..... edge retention, toughness, and ease of resharpening.
Sorry for rambling on so much. I get going on this issue and I just can't seems to say enough!
Hopefully this is helpful.