Can I soak dried fruit in sweet wine instead of liqueur for use in fruitcakes?
A good quality ($20 or so) sweet Port, Madeira, or Sherry could be lovely, and add a delicious flavor note of its own. Make sure it's something that tastes good by itself, with a flavor that appeals to you, complimenting a piece of cake.

Note that these are so-called "fortified wines" — they are distilled to a higher alcohol content. Historically, this was done to achieve a long shelf-life without preservatives, so they're more like spirits. Unlike regular "corked" wines, an opened bottle of fortified wine can last a long time, so the cork is made as a stopper that can be easily resealed.

I don't think you'd get good results with a moscato or such. I also wouldn't skimp and buy a cheap (e.g.: Taylor) bottle of Port — that would be like using cheap, imitation vanilla extract! Spending $30 to get a high-quality flavor that you enjoy, is money well spent.

This kind of wine typically comes in both sweet and dry variants. If you're making an entrée sauce, you probably want a dry wine. For fruitcake, be sure to select a sweet variety. Sometimes, they're not specifically labeled "dry" or "sweet", so you need to read how it's described the label, or ask your vintner for a recommendation.