Is the problem of determining whether a CFG generates a string in the form 0*1* decidable?
Yes it is decidable.
We can construct a total Turing machine M that on input $G$ (where G is a CFG) checks whether it generates at least one string in $0^*1^*$.
Let $G_1$ be a regular language such that $L(G_1)=0^*1^*$.
Note that the intersection of CFL and a regular language is indeed a CFL. And hence a CFG for the intersection of $G$ and $G_1$ can be constructed. Call the constructed CFG $G'$. Also, the emptiness problem for CFG is decidable and hence just check the emptiness of the constructed CFG $G'$.
If it's empty, G doesn't generate any string in $0^*1^*$; and likewise if it's  not empty.