I don't think the artifact approach is unambiguously better. Sure, "consistent deployments on two different Linux systems" is important but you can achieve that with rubygems along with the extra flexibility that distributing the packages as source provides.

Two approaches you can take:

1. bundle package will package up all of your installed gems, which you can then deploy with your project.

2. Your build server can install all of your gems, and then you can package up the resulting directory and deploy it - you could also build e.g. an rpm package.