any decent hardware engineer should be capable of doing both. i don't say that he should do it , but he should be able to.
You can not design a system if you have no notion of board layout , how to make transmission lines, where to split ground and power planes , how to route high speed signals , do impedance control on a board , understand what is signal skew , understand how a multilayer board is made , how cross coupling on a board can play a role etc.
the hardware engineer should always assist the pcb layouter, and for the really triscky things the hardware engineer should put down the rules. In order to put down the rules you need to understand what can and cannot be done ( geometries , drill holes , is it goign to be manufacturable ? will the pick and place be able to do that / .
i have seen numerous *mayor* screw ups becaus hardware engineers fetl they were 'too good' to do the 'lowly' board layout stuff.
Where i work it is MANDATORY ( and thats a 65000 emplyee top 4 semiconductor manufacturer. the same goes for the analog chip designers ; they better know how to layout o silicon ... ) to do the board layout for the critical area's yourself and very frequently you do the entire board layout. period.
if i interview candidates for hardware engineer i have two questions
- do you know how to layout a board. - do you know how to solder ?
even thouh we have dedicated persons soldering , i want the candidate to be able to swap a tssop , 0805 or 0603 component all by himself. he can leace the BGA and TQFPs to the soldering persones , but to swap a simple part he or she should be able to cope. you cannot wait half a day everytime a simple resistor needs swapping out ...