Was searching on YouTube, but cant find exact info if it's worth using Sunder charms (Physical or Fire) for summon necro? Do they apply to minions?

Corpse explosion is 50% fire damage

yes

That's an interesting question. I've read that sunder charms applies the prefix name "sundered" to monsters. This is different from facets. I guess corpse explosion is a no brainer in terms of working on sundered monsters, but do they work for minions, and other players in the same team or area? Quite strange how the game can show different names for the monsters for different players.