Some types of warts are more prone to developing pus than others. For example, plantar warts are more likely to develop pus than regular warts.
Genital warts caused by STDs develop pus as well, especially those caused by herpes. Herpes is viral, but I think it's normal for herpes blisters to become full of pus. It doesn't necessarily mean that it's infected. It's a stage that the blister goes through. First it's red, then it swells and fills with pus and then the pus drains and the blister dries up.