My player wants to take rage feats because DS is similar to barbarian rage.
Whether according to the rules allow it or not?
You mean the Defensive stance ability of the Stalwart Defender prestige class and feats with rage as a prerequisite such as Raging vitality and Reckless rage?
No, Defensive stance does not count as Rage for the purposes of meeting these feat's prerequisite. Defensive stance would need to include a clause like »Defensive stance counts as Rage for the purposes of feat prerequisites« for it to work. That they are similar makes no difference whatsoever.