If you mean combine silicon P-N junction diodes with Schottkey barrier type, I am not sure. Certainly increased fwd voltage drop. I have a feeling that the lower PIV would have to be observed.

I spoke with a product engineer from Cree about the SiC Schottkey types they had just introduced. He said that they could be paralleded for increased current but increasing the voltage by putting them in series wouldn't work like silicon P-N types do.
regards,
Douglas