Track record of incidents?

Dancer: none, mojolicious: five in the CVE database. But that might just mean that somebody tracks the mojolicious bugs and nobody tracks the Dancer bugs in CVE.

Which framework advocates more defensive/secure programming and stricter default template language?

Both allow you to use arbitrary template engines. Mojo::Template makes it easier to interpolate escaped strings <%= ... %> than unescaped strings <%== ... %>. I don't know much about Dancer in this regard.

Does the framework work under strict, warnings, strictures, taint mode, setuid setup?

Both work with strinctures. In fact Mojolicious::Lite enables them by default.

(By default?) protection against: XSS, XSRF, SQL injection?

Mojolicious doesn't generate HTML for you by default, so there are neither vulnerabilities nor safeguards against XSRF.

default admin user/password

You're kidding, aren't you?