The idea of not substituting chocolate chips for chocolate is based on what the other answers say: that chocolate chips have different ingredients (usually a substituted fat in addition to or instead of cocoa butter) than regular eating chocolate.
That is true for many brands.
However, some brands of chocolate sell callets, drops, or chips which are exactly the same formula as their bar chocolate. One such brand available in grocery stores is Ghirardelli. Caullubet is another, although not a grocery store brand. The "disks" from many quality chocolate makers such as Del Rey are also their regular quality chocolate. The form factor is to facilitate melting.
If you know the chocolate is real chocolate, you can use it for any application suitable for real chocolate. Of course, its good to read the label, and know the cocoa percentage and so on for taste, but real chocolate is real chocolate.