Does the electrical conductivity of a wire affect the strength of an electromagnet?

The strength of the electromagnet depends directly on the
current (amps) in the wire that the coil is made out of. 
That current is going to be determined by the voltage of the
battery or power supply that powers the magnet, and by the
resistance of the wire.  So yes, the properties of the wire do
have a direct effect on the strength of the magnet.  If you
tried to make an electromagnet with a coil of wet spaghetti,
it would work, but you would need a humongous power supply
to get any significant strength out of the magnet.