Ok, The Eternal Boss Summoner Hard Mode summons in the hard mode versions of the Ark Eternal Boss Tiers, These guys have increased HP,Damage, and Damage Reduction plus immunity to all debuffs, and an increased Despawn timer to 45 mins to allow for the added difficulty.

Eternal Boss Summoner Normal= the Same summoner we've always had, However of note is the fact that the vanilla bosses summoned from this and the Vanilla boss summoner are EXACTLY the same.

Vanilla Boss Summoner= Simply summons Vanilla bosses if you have Elemental expansion installed. Same exact ones as the Eternal boss summoner normal does.
The Reason for the two is so if a server admin wants to disable the Eternal Bosses but keep the vanilla ones they simply have to disable the Eternal Boss Summoners via the INI configs for them and allow the Vanilla one to remain useable. THAT is the ONLY reason this structure exists aside from as a proof of concept that a structure referenced in one mod could be crafted in another.