Will these interesting new summons be able to be killed via death spells and fogs?

Yes, except the smilodon summoned by Animal Summoning V. This one is an HLA.

Is Animal Summoning V going to be a druid HLA only or can clerics acquire it also? Cleric HLAs are really awful compared to other classes.

Sorry just read in the progress report for v6 that it is a druidic HLA so my question has been answered.
But cleric HLAs still suck
How about a cleric Improved Animate Dead HLA that summons a Skellie Lord with that then allowing an Advanced Animate Dead that summons a Skellie Warlord. It would work like Power Attack allowing Crit. Strike.

Clerics will also have access to a new HLA which is not available to druids. It's a duplicate of the new mage spell "Foreknowledge". We may add more as the mod is in progress.

The ability to summon skeleton lords, however, is exclusive to single class necromancer protagonists.