Mixing them together would give you a sauce (if incorporated properly first). It could be an interesting new thing if you need it, but I can't imagine that many places to use it.
For me, this is clearly intended as a Tiramisu recipe, slightly non-traditional. Somebody left out the lady fingers. You mix the first ingredients to make moccha, then pour it over the lady fingers.
For the cream, there are two possibilities. One is to use all ingredients. Beat the yolks with the sugar to ribbons, add the mascarpone, then slowly add the just-melted chocolate. Fold in the eggwhites beaten to soft peaks. Put over the ladyfingers, and when hardened in the fridge, sift cocoa powder over it.
While this is more likely, I don't see cocoa powder in the ingredients either. Also, so much cocoa might be so strong as to dominate the subtle taste of white chocolate. So you could make the same cream, leaving out the melted chocolate. Then, when the tiramisu has set, cover with grated white chocolate. This is also easier to make, if you are not experienced making creams and working with melted chocolate.
Update I made the recipe yesterday, now it has set after a night in the fridge. I put 90 g of the cream in an ice cream cup, and poured 30 g of the coffee mixture on it. Then I layered the rest as a normal mascarpone, using storebought lady fingers.
The version in the bowl could have used improvement. Some of the liquid found a way to flow to the bottom of the cup. The rest of it stayed on top, where it made a not-so-appetizing surface, slightly seeping into the cream. It did harden in the end, but it is not something a master pattisier would have made. If you insist on using it this way, you should do something else. For example, you could make a ganache by using 200 g of chocolate and 75 g of coffee, instead of the other way round. You can throw in a bit of instant coffee if you want a stronger taste.
The tiramisu looks like a standard tiramisu. It layered well, the amount of liquid was just enough to soak two layers of ladyfingers. All in all, it seems like a good recipe. I have not eaten it yet, but I am certain it will taste delicious.