I have two Bats and two Nesika. For a hunting rifle the tolerances are so tight that debris in the bolt could lock it up. Also do you really need a custom action for hunting? They are well built and very smooth. I have several 700's that are custom and are excellent to build a rifle off.
I have a spiral fluted bat VR action. I have spent over 100 days with it in the field over the years. mostly in the fine grit of the high desert around us. tight tolerances and grit is a total and complete non issue for me. The conditions I hunt in with this gun is such that a fine grit of dust ends up covering just about everything at the end of each day. every couple of days simply wipe off the bolt and you will be fine. Its really no different than any other gun in those conditions. even on those you will probably want to wipe off the bolt.
as for a custom action for hunting?? I say YES! if your spending the money for a good gunsmith, barrel, bedding etc. why put all that money into a factory action, or worse yet pay a smith to "true" it. just spend a few bucks more and have something to be proud of. and if you ever want to sell it you will get most of your money back. a trued remington might be worth even less than a non monkeyed with one.