Want to knit this sweater with different yarn

[Momtopands]

I wanted to knit this sweater for my daughter but it the pattern only goes up to size 4: http://elann.com/ShowFreePattern.asp?Id=138024. I found this similar pattern, that has larger sizes, http://www.berroco.com/exclusives/po.../polkadot.html. Both call for worsted weight yarn but the two patterns have yarns made of different fibers. Is it ok to use worsted weight yarn that is not the same fiber as what is in the berroco yarn?