Firstly, so as not to confuse the issue, ULS is generally taken as being the same thing as Limit State Design. I know that there are two basic limit states, Ultimate & Serviceability but scaffold design is normally carried out to a working stress design. Whether it is only some designs or most designs, I don't know for sure but I have a feeling that it is most. TG20 was produced to give a pseudo version of working stress design based on and complying with limit state design so that the simple minded scaffold designer like me can relate working loads to working capacities.
Secondly, I think that the current gamma factors in the uk for permanent actions in EN1990 are 1.35 & 1.5 rather than 1.4 & 1.6. When I do steelwork design, I consider up to 7 different load combinations with different favourable and unfavourable gamma factors so it tends to get a bit more complex than just putting one factor into the calculations. That mostly affects continuous beams rather than simply supported ones though.
Thirdly, the manufacturer's data sheets show allowable capacities not ultimate capacities. Like I said, secondary effects within fabricated elements like scaffold beams are significant. You need to analyse the beam with the actual configuration of span and loading using the material gamma values to assess the capacity of individual members and joints to deal with the stresses produced by the factored loads. That is not quick or easy to do and is one of my problems with having to use limit state design on scaffolding. I have used limit state design for around 40 years for concrete and steel structures and whilst it has become more complex since CP110 first came out, it is reasonably easy to apply to building structures.
One final issue is that with a system like Cuplock being supported by a beam, the standards may land on chords away from nodes and that has to be considered and defined on the design drawings - this is the case whichever design method you use but it probably means that you shouldn't be simplifying the loads to udl's if you are working on limit state design.