Your math is correct. If you make $100K and pay that out entirely as wages, your S corp will be able to do a 25% match on $100K or $25K.
Note that this means you'll also get a K-1 from the S corp that shows a $25,000 loss. (The loss coming essentially from the $25K SEP contribution.)
For what it's worth, you're probably not saving money by jacking your salary so you can jack your pension. That 15.3% payroll tax "load" you pay is just too costly. Better to use a smaller salary if that's reasonable and accept a smaller pension.
E.g., if you pay yourself $40K and do 25% of the $40K so a $10K SEP match, you do short yourself that other $15K of potential SEP contribution.
But you'll be saving paying roughly $9K in extra payroll taxes.
Obviously, you need to be careful about the salary you set. It needs to be reasonable. The Bureau of Labor Statistics website can help you there. And we've got a table of approximate average S corporation salaries for around seventy industry categories here:
http://www.scorporationsexplained.com/average-s-corporation-salaries.htmP.S. One other thought: Health insurance probably counts as wages if you do the bookkeeping right. E.g., if you pay yourself a $40K base but then also provide $10K of health insurance, you only pay payroll taxes on the $40K but you make the 25% contribution on the sum of the $40K and the $10K... so $12,500.