Following Dick Stevens recommendations for the Kallitype I would use it after fixing on the other hand Sarah van Keuren the author of A Non-Silver Manual sees no benefit in using EDTA with Van Dyke. To quote her:
"It is possible that EDTA salts in water could work as chelating agents to remove residual iron salts, but preliminary tests by photographer John Woodin and myself have not confirmed this." from http://www.alternativephotography.co...-vandyke-brown

Dominik