We do not regard compatibility with other numerical libraries as a priority.
However, other libraries, such as Numerical Recipes, are widely used. If somebody writes the code to allow drop-in replacement of these libraries it would be useful to people. If it is done, it would be as a separate wrapper that can be maintained and shipped separately.
There is a separate issue of system libraries, such as BSD math library
and functions like expm1, log1p, hypot. The
functions in this library are available on nearly every platform (but
not all).
In this case, it is best to write code in terms of these native
functions to take advantage of the vendor-supplied system library (for
example log1p is a machine instruction on the Intel x86). The library
also provides portable implementations e.g. gsl_hypot which are
used as an automatic fall back via autoconf when necessary. See the
usage of hypot in `gsl/complex/math.c', the implementation
of gsl_hypot and the corresponding parts of files
`configure.in' and `config.h.in' as an example.