Further testing...
Booting with just one disk, managed to get OpenE online. Then added the disks one by one rescanning each time. All the disks detected (almost) correctly, but the arrays remained in Degraded mode and no indication could be found as to whether they were resyncing or not. Sitting and waiting did not help, they remained in degraded mode

Interesting was that prior to this, the devices listed as S000, S001, S002 and S003. When bringing them on "hot" they listed as S000, S002, S003 and S004.

Tomorrow I will be scrapping the lot and starting from scratch with the latest OpenE version on the site, as I am a couple of minor revisions behind. If I can't trust the darned thing to boot up if a disk fails then it's not much cop! There must be something amiss. Email alerts also failed, even though on initial setup I did receive the test email. That one may well be junk-filter related, though, and requires further investigation.