Basically yes any derailler is just a slave to the shifters i.e. all the indexing (clicky bits) are contained in the shifters, so with friction shifters any derailler should work.
However you will need to be aware of the 'range' of gears, depending on how many gears/speeds your cassette/freewheel has. i.e. your friction shifers & derailler (made for 5,6 or 7 speed) may not have the adjustment/changing range or a 8,9 or 10 speed cassette.
Also the limit screws on a derailler designed for 8,9 or 10 speeds may not be able to be adjusted for a 5,6 or 7 speed freewheel
FYI: Older style gears/cogs (5-7 speeds) tend to be freewheels where the ratchet system is contained with the gears/cogs which are screwed into the wheel hub and the new/current system is the the rachet system is contained in the actual hub and the gears (cassette) are fixed via splines and a locking ring(Hope this makes sense)
Probably best to post the actual intended parts to acertain compatability
You wil also need to check if your steel frame was made for 700C (present size) wheels or the older 27 inch as this may dictate wether you'll need longer reach brakes etc