Yes, this い is the same as い as in だい or がい. From 明鏡国語辞典 第二版:
In modern Japanese, Definition ② (non-questioning sentence-end い, such as ...
「～～だろうが」 is an accusatory sentence-ender used primarily by male speakers. The 「が」 is a particle.
「がい」, though not too common, is an emphatic and tougher-sounding version of that 「が」.
Likewise, for emphasis, 「か」 for questioning becomes 「かい」 and 「だ」 for affirmation or declaration becomes 「だい」.
Though 「かい」 and 「だい」 are far more common than 「がい」, I do not ...
Well, generally every language has some quirks in its grammar, but as for your examples, を is the only option and に is never used. I sense from your statement "I would've thought に would be used in place, but instead を is used" that you may think or be taught that case particles each represent some kind of "universal" trait, but they are actually decided by ...
The origin of your confusion is both grammar and vocabulary.
This sentence says:
"I applied a ton of その薬の濃度をメチャクチャ濃くしたヤツ to the ゾンビ達の歯や爪."
As stated by @user3856370 in the comment, the 「ヤツ」 refers to the highly concentrated version of this drug. It does not refer to the zombies at all....
Here's the breakdown:
ほっぽる: a colloquial godan verb that in this context means "to leave (alone)"
ほっぽって: the te-form of ほっぽる
ほっぽっておく: the te-form followed by the subsidiary verb おく, which means "to do something for the time being" here. See this question or this article.
ほっぽっとく: the contracted form of ほっぽっておく. See this answer.
ほっぽっといても: the temo-form of ...
You already seem to vaguely understand the difference, but to summarize:
noun + ～を聞く = I hear [noun]: You hear a sound/music/story/etc. 窓が割れるのを聞いた means your heard the cracking noise.
clause + ～と聞く = I hear that [clause]: You hear some fact (via conversations/news/etc). 窓が割れたと聞いた means you heard the news from someone but did not hear the noise itself.
I read that に is used for indicating places of existence, target recipient [of something], the occasion, or the source of receiving an item. (There may be some I have missed.) I also read that を is for objects of a transitive verb (meaning a verb that needs something to receive the action it indicates). If I remember or know correctly, の is used before a ...