Good question mate. There are a bewildering array of different knife handle materials to choose from! Some good, some not so good. When it comes to doing a custom knife, generally you want to use a nice looking material. But nice looking doesn't always mean ideal for the job. I'd say that most synthetic handle materials like Corian, G10, Carbon Fibre etc etc will be ideal from a meat hygiene perspective, but there are some natural materials that are fine as well, Birdseye Maple is one that comes to mind, handle material of choice for the Alan Wood/Ray Mears knife as it is good for use around food stuffs.
There is also a process called Stabilising which involves (as a basic description) placing natural materials, wood, antler, horn, even fossilised mammoth teeth and ivory into a vacuum and then impregnating it with plastic resin. The process effectively makes the selected material impervious to moisture and shrinkage. It's a great way to use materials that have nice looks but would normally be too brittle or full of holes for anything useful like burl wood and rotting woods like birch that taken on interesting colour schemes. The process naturally fills up all the air pockets in the grain and again makes them more hygienic in use.
Micarta is a term that describes a material that is made using strips of cloth, linen, denim, old army trousers, canvas, loden etc etc. You mix up some fibreglass resin and soak the strips in it and then just keep layering it all on top of each other until the desired thickness is reached. It is then clamped as tight as you can and left to set. Once set, you have made a plasticised material of a certain length, width and thickness that is very resistant to moisture. For example, my gralloching set that i posted has Ivory Linen Micarta scales, they look nice, resist the moisture, and are washable.
As for steels, there's an amazing amount to choose from, some good, some bad. Butchers of old only had carbon steel blades and if offered some of our new stainless steels would probably turn there noses up at them. People worry about carbon steels as being un hygienic, but if you follow basic levels of hygiene and wash/sterilise them after each use you shouldn't have a problem. They are however a bit more work to look after, so if you're the sort who goes out stalking, gets himself and his gear wet, comes home and ditches everything that doesn't need to be in a locked cabinet in the garage and forgets about it all for a week then carbon steel is Not for you!