Is (1 bit HW signal) XOR (8 bits PRNG output) sufficient for a HWRNG?
No, this is not a good way to whiten an HWRNG, and it definitely won't give you anything like true randomness.

It is true that the XOR of two independent bitstreams will, indeed, be at least as random as either of the original bitstreams.
However by XORing only one bit of hardware randomness into each byte of output, you're effectively padding each bit in the hardware RNG stream with 7 zero bits, making it very non-random even if the original unpadded hardware RNG was perfectly random.  You're also not doing anything to fix any possible biases in the hardware randomness except for XORing it with the pseudorandom bits.

In particular, this means that, if an attacker manages to discover the internal state of your PRNG (e.g. via statistical observation of the output, seven eighths of which is completely unaffected by the XOR), then they can trivially predict all but the lowest bit of each byte in the XORed output &mdash; and may even be able to guess the last bit with better-than-even probability, if the HWRNG output has less than 100% entropy.

(That last part would still apply even if you fixed your scheme to XOR each bit of the PRNG output with a separate HWRNG bit.  To actually achieve proper whitening, you really need to mix multiple HWRNG bits into each single output bit (preferably non-linearly), or at least feed them through a properly designed entropy pool.)