Uh... you know one of Hitlers 'something else' was the same reason as your seeders (Hitler called it Lebensraum, which means 'living space'), so you aren't really right about them being any worse, they are just doing what Hitler did so.
And to be fair, I would say that killing someone for their land is less evil than killing them because they are of a different race, seeing as how dozens upon dozens of our wars have been to kick people out and take their land. Genocide because you think a race of your own species doesn't deserve to live is infinitely worse
What the seeders are doing is exactly what Hitler did. They are killing off a race (or rather, species in this case) to make room for their own race (species in this case), and when you think about, both think the others are less important (Clearly the seeders feel superior and more important as they are displacing them to make way for themselves)
Its hard to say they are worse than Hitler because we don't really understand what went on inside his head and probably never will. Or, you know, its possible he was completely sane and it is just the nature of neb to butcher each other . Really, the only way you can say someone is worse than Hitler would be to go on facts and figures along, and that isn't too useful. I suppose you could do it by comparing him with another evil dictator such as Stalin, but again we don't entirely know what was going on (then you can make the argument that Stalin was Hitlers fault because Stalin became obsessed with the idea that the Nazis would invade the USSR. Then you can argue Stalin thought he would be the lesser of two evils because Hitler also hated the Russian people and might try to kill them all like he wrote in Mein Kampf, and Stalin wanted to protect his people and thought the only way to do so would be through tough love... Very, very tough love.)