When you transfer pokemon holding items do they keep them?
Also if you transfer Onix while he is holding metal coat does he evolve?
No holding items may be transfered. Pokemon like Onix cannot be holding the item, and will not evolve. Others like hauter and machoke that evovle when traded (no item required) also will not evolve.
A) trading ISN'T transfering, so evolving this way is impossible
b) holding items is possible between III-IV gen
c) but isn't between IV-V gen