If its pure hentai... like... for example... the creatures spew addictive mind altering aphrodisiacs from their "definitely not cocks", that turn their victims into horny, super eager, happy happy cock worshippers, and there are no traumatized, suicidal, etc, victims angsting about it... then its fine...
If its intended to establish the "badness" of the bad guys... like in goblin slayer for example... then a more realistic, traumatizing depictions can be fine too... As long as it don't get too graphic, and the story don't focus on it too much, just doing whats needed to "establish" the setting or creatures... it should be ok... but I don't want to read too angsty stories...
Mixing the two... not a good idea...