Sure, Nidus is a good candidate for Umbral build because he benefits from Armor, Health and Strenght, at the same time he just needs extra range for his larva ability and energy efficiency is not an issue on this build since he regains all energy back when hitting 4 enemies with his 1th ability, and if he hits more then 4 enemies he actually gains energy with each hit.
So this is the standard build I'm using:
Blind Range is leveled only to rank 6, even "only" 244% power strength is kinda overkill for 99% of Warframe content, efficiency is lower but it still enables for some mistakes. Adaptation greatly increases suitability and Hunter Adrenaline ensures that if Nidus does take a pounding he will have energy to pound back.
Now for starchart content I'm actually going to leave Blind Rage slot empty because it kills enemies too fast and I can't collect stacks 🙂
And this is a build for long survivals I'm using:
On this build Blind range is at rank 10 and I used rank 4 Hunter Adrenaline and rank 4 Strech to compensate.
In high level content Nidus is going to tank a lot of damage so due to Hunter Adrenaline energy will almost always be toped off, range got a really small reduction. Due to higher ability strength I get more damage on his 1 and more healing from his 4 and I need both of those to survive.
And this is a Valkyr build I'm currently working on, once again Valkyr benefits from Armor, Health and Ability Strength and other then that she basically just needs some durability/efficiency.
Now Arcane Energize is kinda overkill on this build, it really doesn't need it, Valkyr gains energy when she get's damaged and when the energy is full player uses her 4 gains immortality and kills stuff and gets healed in the process... repeats. There are a couple of things to watch out for, nullifier bubbles, energy leeches... but that's what I like about this build, it's not just immortal build like Inaros... player has to play smart to make use of it.
Here I do use Steel Charge both because of extra 4 mod space and because I mainly use melee with this build, with Eternal War augment I usually have to cast Warcry just once and it lasts for entire match. I modded her talons with Primed pressure Point, Sacrificial Steel (although just True Steel is fine too), Organ Shatter, Gladiator Might, Shocking Touch, Molten Impact, Berserker and Drifting Contact. Valkyr gets healed for 5% damage she does with her Talons and since radiation ignores 75% of the armor she will always deal enough damage to heal herself really fast.