no

(Small Spoiler Warning. Also Sans is dead)

They both start with an N.
They both are smol.
They both killed someone.

Now, for the evidence.

Both Niko and Ness have four letters.
They both have wielded a weapon. A crowbar and a baseball bat.

Baseball bat = baseball
Crowbar = half-life 2 = half life

Baseball was invented in 1839.
A half-life is the amount of time needed for a quantity to become half of it's inital value. Half of 1839 is 920, rounded up.

What is 920?
920 is a Wisconsin area code that covers much of eastern Wisconsin. How does this relate, you might ask? Because in eastern Wisconsin, there is Green bay. In Green bay, there is a Wildlife Sanctuary that houses owls.

Owls. Their eyes can "Glow". You know who else's eyes also "glow"? That's right, Niko!
Why is this emportant? Owls are primarily active during the night, and earthbound starts during the night. There's more, though. Owls can fly. What else can fly? Eagles. A country in Earthbound is called "Eagleland". Coincidence? I think not.

If we look at what was made in the 1920's (the one comes from the singular cracked baseball bat ness obtains at the beggining of Earthbound) we find that Kool-aid was made in 1927.

Kool-aid. Kool-aid's mascot is Kool-aid Man. The Kool-aid man is red. You know who wears red? Ness, with his cap. Not only that, but if we re-arrange the letters in "Kool-aid Man" we get "Mad- in Kolo", which sounds like "Made in Kolo".

Kolo is a town on the Warta River in central Poland. It's total population is 24,034 (as of my knowledge). If we were to divide this number by 1927, we get about 12.5 . If we assume this is a half-life and double it, we get 25, which is 2.5 less then the estimated time to beat Earthbound (From Howlongtobeat). If we take Oneshot's estimated time to beat (4.5 hours) and subtract 2.5 hours from it, we get 2. The hours should cancel out, and I'll show you why.

We now have a 2.
We are talking about Niko and Ness.
Two people.

NIKO IS NESS CONFIRMED

But why would they be the same person, you might ask?
To that I answer that there doesn't NEED to be a reason why. It can just be. Like how the color red is called "Red". There is no reason for the name "Red" to be given to red, it just was.

How did I, a very intelligent person find this out?

Well, ya see...
I. Need. Sleep.