I am not sure if the answer is still wanted...
Under your assumptions hypothesis 2 is correct. The state of photon pair in this case is $\left|\psi\right>=\frac{1}{\sqrt{2}}\left(\left|H_1H_2\right>+\left|V_1V_2\right>\right)$ The probability of a coincidence to be detected with polarizers oriented, say vertically, is $P_{VV}=\left|\left<V_1V_2|\psi\right>\right|^2=1/2$. This means, that half of the pairs give rise to coincidence counts, so the total pair production rate is 600 pairs/s. This may be understood like this: if the vertical polarizer is put in one channel, the presence of similarly oriented polarizer in the second channel will not reduce the number of coincidences since the photons are perfectly correalted in polarization, while of course it will cut off half of the single counts. The feature of this particular Bell state is that this is true for any orientation of polarizers, if both are rotated at the same angle.
The first hypothesis will be true, for example, for detection of pairs in completely unpolarized state described by the density matrix $\rho=\frac{1}{4}\left(\left|H_1\right>\left<H_1\right|+\left|V_1\right>\left<V_1\right|\right)\otimes\left(\left|H_2\right>\left<H_2\right|+\left|V_2\right>\left<V_2\right|\right)$, where only quarter of pairs will produce coincidences in the described situation. Locally, i.e. using data from a single detector only, these states are indistinguishable, since the reduced single photon density matrices are identical. However, the Bell state is polarized (in fourth-order in the field), which is revealed in intensity correlation or coincidence measurements. This is an example of what is sometimes called "hidden polarization".
