Last season, the Seattle Seahawks carried five defensive ends, including Demarcus Dobbs. (And hybrid fullback Will Tukuafu but honestly, that's more "gimmicky" than anything else.) Dobbs had 11 tackles with the Seahawks last season and has zero sacks in five NFL seasons. He is currently still a free agent.
If there is one real camp battle for a roster spot though, it probably belongs to Clemons and Robinson. The two players are fighting for one spot most likely and it really comes down to age+experience vs youth+potential. And don't be fooled: Seattle likes Robinson .