Resolved issue

I finally figured it out - been at it for hours!
With the default packages openssl won't update to the latest required version - this is how I got past it.

First I installed the Axivo package:

    rpm -ivh --nosignature http://rpm.axivo.com/redhat/axivo-release-6-1.noarch.rpm && rpm -ihv http://centos.alt.ru/repository/centos/6/x86_64/centalt-release-6-1.noarch.rpm

Then, updated yum

    yum update -y

(Source: http://dynaboot.com/blog/creating-rpm-package/)

Next, I enabled the repo with this command:

    yum --enablerepo=axivo clean all

Finally I updated openssl

    yum --enablerepo=axivo update openssl*

(Source: https://www.axivo.com/resources/openssl-setup.2/update?update=3)

Installing proftpd with yum install proftpd finally worked now. After frekin' hours. Hopefully this helps somebody else - I tried to include most of the search terms that I used throughout the night.

Fantastic!