Good exploring, Yogi. Deserves upvote.
Here below is the explanation.
They are two, very different, words but very closely related.
Neeti is - 'code of conduct'.
Dharma is - 'to hold on to what is true and just'.
To understand Neeti & Dharma better, one needs to explore the relation between them.
Here below is how they are related;
[Keep in mind the above definitions, while investigating their relationship.]
It is Neeti to create a code of conduct that upholds truth and justice.
It is Dharma, to establish, i.e, to make prevail, that code of conduct.
Hope your exploration is satisfied.
Keep going, and share with us, whatever new you find.
I have marked this as my favourite, question.
As far as the demand for citing from scriptures; what I want to aprise the readers about here is, what I have said in the answer above, is an extract of what I have read and contemplated through the years & further it is not feasible to establish right here through scriptural evidences, how I have arrived at that answer, because; the concepts of Dharma & Neeti have been discussed & debated since times immemorial in innumerable texts. If I have to show, how I derived that answer, I will have to write a thesis then! right here! It has taken me nearly my life time to arrive at that result. But anyway I will cite one quote from a scripture, which shows that Dharma & Truth go hand in hand. In Hinduism, there is a genre of texts called 'Dharmashstras', which are exclusive treatises on Dharma stating the duties, responsibilities and ethics to oneself, to family and as a member of society. This quote is from "Vashishta Dharmashastra". But before that, I would like to discuss on what @Yogi has said and show that Truth & Justice are not different. They are the two view points of the same thing.
Now, @Yogi said;
Quote "justification is result of human analysis" Unquote.
As I said above, Truth & justice are the two different faces of the same coin. They are inseperable. They go hand in hand. They do not exist in the absence of one another. Now let me show where the above statement that "justification is result of human analysis" goes wrong.
Justification is of two kinds; depending upon who justifies; because the Justifier is of two kinds.
The two kinds of Justifiers are: one is the Ignorant & the other is the All-Knowing.
The justification made by the ignorant is always wrong and so unjust.
And the justification made by the All-knowing is always right and so just.
This also shows that, what is wrong is unjust & vice versa. And what is right is just & vice versa.
So now the question arises as to what is right?
The answer is; Truth is always right. Truth can never be wrong. And nothing else can ever be right. What is wrong is not Truth. And above all;
Only an All-knowing person can do justice because only he can arrive at the Truth.
Now coming to the scriptural evidence.
The Vashishta Dharmasutra hints that, Dharma and Truth, and now Justice [It has been shown above, i.e, Truth & Justice are the two different faces of the same coin.], all three, go hand in hand. In Chapter-30, Sutra-1, it says; http://www.hinduonline.co/vedicreserve/kalpa/dharma/vasishtha_dharma_sutra.pdf
"धर्मं चरत माधर्मं, सत्यम वदत मानृतम्।",
which translates to- "Take the course of Dharma and not Adharma, speak the Truth and not the Untruth". It is said so because the two i.e, Dharma & Truth do not exist without one another. And from above discussion we have seen that, Truth & Justice are the same thing. So,
Dharma is upholding of "Truth & Justice".