I suspect a number of these birds could be Forbes-Watson's. I was a bit concerned about the date but I checked a blog written by my late friend Rob Tovey, who used to live there, and found a couple of posts confirming they're still around in mid- to late October. Soon after this they disperse - I don't know where - and on my first visit to the Salalah area in early Jan 2015, I didn't see a single one. This is contrast with my second visit in late May the same year, when I saw literally hundreds. This was not only at the known colony at Taqah cliffs but also flying low over the ground at Jarziz Farm.
What was obvious on those birds was the very prominent pattern of scaling on the underparts, with more obvious pale edges than on Pallid, contrasting with the pale throat (less extensive than on Pallid). In the series of images taken by Jens Eriksen below, this is visible on some of the better shots, e.g. the last one, as is the dark saddle mentioned by Deb. On closer inspection the dark saddle is the result of scale-like dark greenish-brown feathers on the back. This can be seen in image no. 11.
http://www.birdsoman.com/Birds/079-Swifts/ForbesWatsonsSwift/ForbesWatsonsSwift.htm
Another important feature we can observe is that FWS doesn't seem to have any white on the forehead. Compare the FWS images from the link above to the images of Pallid here:
http://www.birdsoman.com/Birds/079-Swifts/PallidSwift/PallidSwift.htm
None of the Pallid images come from Dhofar but they do pass through.
There is the additional issue of confusion with
pekinensis. I'm not sure how common this taxon is in the Gulf. The 2nd slide below shows how this taxon can show a dark saddle and even a green tinge on the median and lesser coverts. However, if you look at the 4th slide, the underpart feathering seems to lack the pale edges seen on FWS.
https://www.smugmug.com/gallery/n-R4rMj/i-hBWjLBw
If I had a go at your images, I would say:
1st post -
1. not sure but probably not Pallid, as the forehead isn't pale enough and there's a bit of a saddle - however, pale throat seems to come to a point, supposedly a feature of FWS as per The Birds of the Middle East, and there might be a green patch on the secondaries
2. probably FWS but can't rule out
pekinensis - back is a bit green-tinged though
3. same as no. 1 but again, feathering on saddle looks a bit green-tinged
4. FWS - the green panel on the trailing edge of the wing matches image no.11 in Eriksen's gallery, white fringes to barring on lower belly and UTCs
5. not sure - could be Pallid
2nd post -
1. looks a bit
pekinensis
2. same bird? - a couple of pronounced pale edges to secondaries though
3. FWS - scaly back with pale fringes, same green panel on wing
4. not sure - the underparts feathering lacks pale fringes, rather extensive pale throat suggests Pallid but forehead not pale enough
5. I think this is FWS - it has that same green panel on the secondaries, pale edges to inner primaries and a few secondaries
Any further input welcome, as I'm on a learning curve here.