Dura-ace downtube shifters and Ultegra rear mech

I've just bought myself a new Ultegra rear mech and a pair of braze-on
dura-ace shifting levers (downtube) ....ok call me old fashioned.....I
noticed though that they say these shifters should only be used with
Dura-ace rear mechs......Has anyone treid to use these levers with any
other mech and if so what problems did you encounter...if any??
Cheers,

Jon.