Assuming that the raised beds have no solid base, then yes, an amended topsoil or garden soil mix is the recommended filler. Additions of compost annually are always suggested to maintain levels of organic matter and keep the soil life happy but you will very likely need to fertilize routinely as well. Compost just does not have high enough nutrient levels to be sufficient for plants that draw out a lot of nutrients to reach maturity like most veggies or other annual crops.

In Mel's book, the soil mix is equal parts compost, peat, and vermiculite or perlite. You might want to add some vermiculite depending on the quality of your topsoil. It can vary a lot. Where I live, topsoil is sometimes just poor quality dirt.

Vermiculite is very unnecessary in any sort of raised bed soil (even with SFG!!). It should also be pointed out that the square foot gardening soil mix was developed for a very specific intent, which is not at all the same as a traditional raised bed. Nor is it highly recommended by those who do a lot of raised bed gardening (it is really just a container mix, not even a very good one at that, and unnecessarily expensive to use for a raised bed when a much simpler approach will work equally as well!!)

Whether it's a good growing medium depends on the type of topsoil. The industry's advertising campaigns have expanded the definition of the term far beyond its original meaning to include any soil taken off the top, even lifeless dust scraped off gravel pits. Topsoil apparently sells better than filler dirt. It wouldn't hurt to confirm the reputability of the company and the product you plan on using. Also, a guarantee against common noxious weeds is advisable. In my neck of the woods (where are you located?), crabgrass or nutsedge breaking dormancy after a vegetable garden is established would force the gardener to start over. I'll second GG's comments re compost, fertilizer and overpriced mixes based on vermiculite.

"A small amount of compost" doesn't sound like a lot. Unless the soil was high in organic matter to begin with, I'd be looking at 1/4-1/3 compost by volume. It's your best chance to amend easily and deeply so make it count. If you haven't looked at this soil yet, go inspect before buying. If it looks like you'd want more compost in it, add some when you fill the beds. If you need a cubic yard or more, consider getting a pickup load somewhere.