"Musalli" is a term that in Lahore and Gujranwala areas is used only for muslim converts from "sweeper chuhra community", these guys were part of the society and spoke punjabi langauge.
Gypsies on the other hand in our region have various designations, they are called "changar", "Pakhiwas" (birds like nomadic lifestyle), Chuggiyan walay (jhuggi people) etc. Their principle language was always a form of "Rajasthani" language and before 1947 they regularly used to travel between Rajasthan and other areas of india through punjab to as far west as afghanistan. They were engaged in the trade of "ghugu goray", "chooriyan", "chhaj" for sorting out rice, "mooray" (for sitting). I remember in my childhood in 80s, I used to buy "ghoriyan" (horses) made of wood/paper/cloth from them. They were also the people who used to come to our annual mela in our village to do circus stuff etc. And many of them actually were "fair skinned" though most of them were dark skinned like indians but they have nothing to do with punjabi "sweepers". Singers like Reshma and Naseebo Lal are from these "Pakhiwas" communities.
In the past I think most of them didn't follow any "mainstream religion" and were like any primitive pagans or animists. I know one community in our Gujranwala who used to set their "jhuggis" annually in empty place along a road in an affluent area of Gujranwala in 80s, with time they started "settling" on that place permanently and made a kachi abadi in later years and now they have permanently settled there (in other words they have done qabza on that empty space around the road). Now they call themselves and their new "basti" as "Nau Mulim town" or "newly muslim town", I saw them in recent times to even participate in 10th muharram jaloos in the past years.
An interesting memory from my life is that when I was child and wouldn't cut my hair or take a showere for long time, then my mother used to say me in punjabi.
"Ja ja kay waal kata tay na, kay tun pakhiwasan wangar naan to toba keeti ay" (there is a punjabi sense of humor in this sentence).
"Go get a hair cut and take a shower, or else have you done "tauba" from taking shower ever in your life like a pakhiwas (gypsy changar)".
I think muslim pakhiwas/changars used to be called "deendar" in our area to differentiate them from the "musalli" which was designation for muslim converts from chuhra/sweeper community.
Here is a funny video of a Baba (called baba kuki) from a village of Gujranwala who is talking about some "deendar" guys teasing him in this video.