Yes Himachal is an integral part of the Indus Valley region as it is the origin of many the Indus tributaries Chenab, Ravi, and Baes. However, it is very mountaneous and has harsh terrain, and there are no IVC sites there as of my knowledge. The IVC region in India encompasses the states of Gujarat, western Rajasthan, Punjab, Haryana, and Himachal.(JaK as well, but that is disputed. This is the most accepted map. Unfortunately, I am nowhere near as skilled at creating diagrams as IP.
As to your question about people, well I have been to HP several times so I can answer that question. HP was a part of Punjab, but has always been culturally distinct, do to its geography and majority Hindu faith. The majority of Himachali people are ethnic Paharis, an Indo-Aryan group native to the Himalayas. Paharis live in Nepal, Himalayan regions of India(Himachal, JaK, and Uttarakhand), as well as AJK in Pakistan. So most Himachalis are similar to people from AJK. Himachal also has a significant Dogra population, and Dogras have Rajput ancestry, so there is also similarity with Pakistani Rajputs.
Keep in mind Himachal borders Tibet, so there is a strong Tibetan influence in Eastern HP. There are several languages in this region similar to TIbetan, such as Spiti and Kinnauri. Of Course, there are a lot of Tibetans as well since Himachal is the home of the Dalai Lama.
Other dialects of Pahari spoken in Himachal are Kangri and Mendeali. Some of these dialects have their own script, such as Kangri, which was historically written in Takri.
https://en.wikipedia.org/wiki/Kangri_dialect
https://en.wikipedia.org/wiki/Pahari_people
https://en.wikipedia.org/wiki/Kinnauri_language
https://en.wikipedia.org/wiki/Western_Pahari
So yes, Himachalis do share similarities with many Paksitani populations. Of course, there are also plenty of people they have nothing to do with , such as Sindhis and Balochis.
Here are some examples of Himachali people.
I hope I was helpful