A unit array is just a list of units. There are lots of ways of creating one, of which the easiest is just to write it.
[unit1, unit2]
is a unit array. Don't get bogged down in arrays here, that is not the problem.
However, if you have an array, you need to use command that take arrays. For example, alive takes a unit, not an array. So you would need to use the commands count or forEach.
In this case, given that the number of scuds can't be that many, forget arrays and just write out the list of units. There is unlikely to be any advantage to using an array anyway.