No, you cannot - currently. A single OpenID cannot be both employer and candidate.
However, it should be possible to implement this and there is no reason why one person could not be both at the same time, or could not be in one role first and second role later.
It is kind of ironic to need two OpenIDs to log into a single site, considering the purpose of the OpenIDs was to reduce the need to create a new identity for each site.
There is already upvoted comment to Jeff's answer in this sense, but perhaps having it as a separate answer (which, off course will be upvoted much more times than the Jeff's one) will make more prominent argument such feature should really be implemented.