Yes, poclbm should gracefully handle it. But also eloipool could handle it by serving out 1 in this special case and use pdiff for any higher figures. When sending the value to the client, just ceil(pdiff,1.0) it? Call it a workaround for poclbm or whatever. Or check client name for poclbm and only serve it to them.
Sending 1 will cause miners to not submit, and thus not be credited for, some (tiny fraction of) shares.
More problematic, poclbm does NOT send its useragent over stratum, so there is no way to identify it.