This weekend I just did my very first century, The Old Kentucky Home Tour, on my hybrid. I only had maybe 6-7 rides over 50 miles all year (and no rides over 25 miles in any previous years dating back to getting my first car). Bike weighed in at 50 pounds as ridden, all gear in bags, bottles full. Full wieght with rider (in gear and helmet) was pushing 300 pounds.
You can for sure do a century on a hybrid.
Ride time was 8:12. average speed 12.8 max speed 37.8
Now I have at least 4 more centuries on my ride schedule between now and the end of October.