Based on my own experiences at various universities, the accounts of colleagues at yet other universities, and what I have gleaned from the instructions that accompany tenure dossiers that I am sent to evaluate, it seems that different institutions have different policies regarding how publications and grants are counted for tenure. For example, policies seem to vary as to whether publications and grants are considered in the tenure evaluation if they stem from Ph.D. research and involve the former adviser(s) as co-authors or co-PIs.
The variations I have seen are (1) everything counts; (2) only those items that post-date the start of the tenure-track appointment count; and (3) only those items that post-date the start of the tenure-track appointment and that do not have ex-advisers as co-authors count. Everything goes on the CV, but what is actually considered in the tenure evaluation may vary.
I was thinking about this recently because I have a new project and collaborative grant with one of my former graduate students, now a professor. We got the grant a couple of years after she completed her Ph.D. and it is a completely new research project, only slightly related to her Ph.D. research. We just started the project, but of course we hope that publications and perhaps future grants will result.
I told my ex-student/now-colleague to find out exactly what the policy is at her university re. what counts for tenure. I am sure there will be a way to explain that this is a new project, even though it involves an old adviser. I am not worried at all that our collaboration will harm my former student's tenure case in the future because she has other grants and independent projects, so she's going to have a strong record and an impressive reputation for her own work no matter what the policy of her university.
But I wondered: In a more marginal case or in a case of a very strict definition of what counts for tenure, is it possibly a bad thing to collaborate with a former student before they get tenure?