No, leyland won't work in boggy ground (fortunately).

There are actually plenty of kinds of willow that will, it is an extraordinarily diverse group of trees. Plenty for you to research there. Several kinds are suitable for hedging.

Alders are another thing happy with wet feet, and again there are a few kinds. Willows and alders are the characteristic plants of carr landforms in Britain, ie, treed boggy places, so those are your main native options.

If you want a conifer, most of them hate swamps (regardless of Scotland appearing to be a huge bog covered in conifers). But there is something called swamp cypress (Taxodium distichum), which I think is pretty hardy but you might need to check. Metasequoia glyptostroboides (Dawn redwood) is another hardy conifer also tolerant of such conditions.

But do you know how Scotlands bogs managed to be covered with Sitka spruce? The answer is that to plant them they have to raise a ridge of soil about 50cm above the surrounding boggy ground, and plant the trees in that. This raised ridge is well drained, and the trees can then start growing in the ridge, and as they reach down into the boggy ground they lower the water table and increase the amount of soil sufficiently dry to grow in. So that is a possibility for you if you wish to increase the range of options. Trees such as birch that commonly grow close by bogs would then become a possibility.