I remember hearing that the episode with shou tucker and Nina tucker was to show the elrics (and perhaps us) what alchemy can become, what the elrics can be (if they perhaps had no, or less morals). That science can be taken to hurt those around us, all for the sake of knowledge or (or maybe just keeping his license). Or something along those lines. That they aren't too different, and it won't take much for them to become monsters. 

but tbh, i saw more similarities between rose and the elrics rather than with tucker. 

Rose had lost her fiancé, and sought to get him back, and the Elrics had done the same for their mother. The only difference is, how they sought to get back their loved onces, Rose turned to religion, and prayed, and did whatever she could to get her love back. The Elrics had turned to alchemy, and sought to find a way, using science and alchemy to get her back. 

And in the end, they were just people who were hurting, hurting that people they've loved so much had left them. Who had wanted back what they had lost, and turned to what they thought could give them back what they had lost. They had both learned in harsh ways, that once people are gone from this world, they aren't coming back again.