Hi Augusto,
I'm sorry you are having difficulties. As to why we focus on Ubuntu, it is exactly for this reason: there are endless variations of distributions and flavors for linux, and in each one of them, the way that packages and other dependencies are managed is completely different. We do everything we can to make AtoM and all of its related resources, including this forum, accessible without costs or membership requirements - you can read more about our business model and development philosophy
here. This means that Artefactual invests countless unpaid hours into bug fixes, release testing and packaging, documentation, tutorials, and forum support.
We simply cannot test AtoM on every single possible combination of O/S, webserver, and database - we do not have the time or resources to prepare many alternative installation instructions or workarounds where packages are unavailable. We prefer to focus on one distribution and do it well based on our experience and skills, instead of offering bad documentation and support for many platforms.
This means that we rely on our community to support each other when users choose to install differently than our recommendations. I hope that if you continue to work with FreeBSD, you might share your installation instructions, tips, and tricks with the community - we will happily add them to our wiki and share them here for others to benefit!
In the future, there are likely development approaches we could take for better abstraction, so AtoM is not so dependant on a particular distribution. Keep in mind that we are working on a project that was started over 8 years ago, with a business model that makes it very difficult for us to get paid for maintenance work (as everyone wants a new feature, but no one wants to pay to upgrade or overhaul a dependency). As such, we have learned a lot over the years, and will likely make different choices that take these lessons into account when we begin to consider AtoM3. For now, we have to work with what we have, as we don't have the resources to overhaul AtoM without support from institutions like yours.
In the meantime, we at Artefactual are unable to offer you support for this particular set-up, as we are less familiar with FreeBSD and don't have the resources to test and document this particular configuration. I would suggest that you try checking the Gearman and FreeBSD resources and forums.
You might also consider virtualization - running Ubuntu (and AtoM) as a production-ready virtual appliance on your FreeBSD o/s. This would allow you to follow our recommended installation instructions and install all dependencies in your appliance as documented.