Marmolada glacier is easy and not so wide, but... It's a glacier and there are many crevasses, even though you can't see (they are covered in snow: the most dangerous one!)
I think if you don't have experience of roped glacier travel, it's better if you take a guide.
Usually the glacier is crossed by a well marked track, and dozens of people pass there every day with good weather...
If you go without a guide, quite surely you'll survive but you get a little risk, and my advise it's to go with someone experienced of glaciers (I remember that, 10/15 years ago, a strong italian climber, climbed up from an extreme-route of south face, fall in a crevasse and died descending from normal route... He was a very experienced mountaineers, but he went without rope...)