Yes, please use 11767 instead of 11125c01. I wasn't aware that we knew the number for the assembly.
Each separate physical element should be a separate LDraw file - so yes, the axle (trivial though it is) should be a separate file. The uNNNN numbers are used where we don't know the LEGO Design ID for the part see here. Regular authors can request (from me) a block of uNNNN number, or I assign them individually as required. There is no inherent meaning to u9081, so please use that for the tyre and u9082 for the axle.
Each separate physical element should be a separate LDraw file - so yes, the axle (trivial though it is) should be a separate file. The uNNNN numbers are used where we don't know the LEGO Design ID for the part see here. Regular authors can request (from me) a block of uNNNN number, or I assign them individually as required. There is no inherent meaning to u9081, so please use that for the tyre and u9082 for the axle.
Chris (LDraw Parts Library Admin)