We need a backup ruckman, albeit someone who is happy to spend most (if not all) of the season playing in the SANFL. They're not easy to come by. Most of them either aren't good enough (which is why they're already playing in the SANFL) or have delusions of grandeur (daring to dream of being 1st ruck and playing regular AFL football).
Graham comes to us on minimum wages and in the knowledge that he is nothing more than a "break glass in case of emergency" type player - should something happen to Jacobs.
We can't afford and don't need a high quality ruckman - Jacobs is capable of filling that role. We just need someone who is capable of doing the task to an adequate standard if our primary ruckman falls over. Graham fits the bill nicely.
As long as all that is really true, that all makes a lot of sense.
A proper backup ruckman does put that whole Jenkins/Smack as the backup ruckman to bed. In fact aside from filling in a KDP, kinda makes Smack look morel like tradebait, with Lynch and Johnstone looking for a game up forward.