Absolutely. r509 (which this tutorial uses) is fundamentally a wrapper around the OpenSSL bindings of Ruby. It doesn't do anything that you can't do without it; it just tries to present certificate generation/revocation/management in a simpler manner.

This is most evident in the OCSP responder, which leverages sections of the Ruby OpenSSL code that have...limited documentation (see: http://www.ruby-doc.org/stdlib-1.9.3/libdoc/openssl/rdoc/Ope...)