Yes. According to the SAS manual "The standard errors computed by PROC SURVEYFREQ are based on the multistage stratified design of the survey. This differs from some of the traditional analysis procedures, which assume the design is simple random sampling from an infinite population." See: http://support.sas.com/documentation/cdl/en/statug/68162/HTML/default/viewer.htm#statug_surveyfreq_gettingstarted.htm ... View more

The Breslow-Day (from the CMH option) tells you that the rate ratios for your strata are the same (p>.05) or different (p<.05). It is only comparing the rate ratios (or odds ratios) for group*response for each level of period. If you are trying to see within group differences (ex: is there a significant change in the rate for group 1), you'd need to do something different, maybe even just plotting the rates with a linear reg. ... View more