The dopings should be unaffected, but evidently these
are "gated diodes" and/or poly-defined, self aligned
(not mask defined at the N+ / active layers). Then
you have the reverse voltage reliability "pinned" by
the thin ox or thick ox's hot carrier and oxide breakdown
limitations, probably lower than the raw junction
capability. Thin ox probably has ratings like core FETs
and thick ox, similar to I/O / ESD devices (of which,
the thick ox diode is probably one standard device).