You can feed High Fibre Horsehage (blue wrapper) to laminitics. Because it is low in sugars I would have thought that it wouldn't affect a fizzy horse too much either. Ryegrass Horsehage is higher in sugars and energy, so not suitable for laminitics and there is always the possibility that it may affect a fizzy horse, although I've not found this problem myself.
Other types of haylage will depend on the grasses used and the time it is cut.
i had my mare on hi-fibre horsehage and hi-fi lite when she went down with laminitis.
my vet was adamant that i should get rubbish hay for her, soak it for ages to leach out all the goodness, and then she could have it. would not let me keep her on blue-bag horsehage.
i've known of one or two horses who went loopy on horsehage, but most are fine.