No, gravitational waves are not emitted isotropically. In the weak-field limit (i.e. far from the sources), the radiation emitted by a gravitational system is determined by the third time derivative of its quadrupole moment, which, being a tensor, needs to be projected along the line of sight to yield a (scalar) energy flux. This projection is what gives the angular dependence to the energy flux.
That you need to consider the quadrupole moment is easy to understand: the dipole moment of a mass distribution is a constant, and can always be set to exactly $0$ if the origin of coordinates is chosen in the system center of mass. The monopole moment is the total system mass, which is conserved (in the weak-field limit), hence the monopole field at large distances is always $-GM/r$, a time constant, hence no radiation. The first physically relevant term is thus the quadrupole moment, $D_{ab}$.
Calling $X_{ab}$ the third time derivative of $D_{ab}$, the time-averaged energy flux in an element of solid angle $d\!\Omega$ in the direction $\vec n$, where $\vec n$ is a unit vector, is (Landau & Lifshitz, Field Theory, vol. 2, Ch.13) is:
$$d\!I = \frac{G}{144\pi c^5}\left((X_{ab}n_an_b)^2 + 2X_{ab}X_{ab} -4 X_{ab}X_{ac}n_b n_c \right) d\!\Omega $$
Obviously, $n_a$ are the components of $\vec n$. It should be obvious from the previous argument that GWs cannot be emitted isotropically.