Hi Sue,
Following Glyn's message I've had a look on the PRO catalogue. These two
piece numbers cover St Davids:
St David Without RG 13/5167
St David Within RG 13/5168
I suggest you do a direct search on the 1901 census site, for Piece
RG13/5168 Folio 19 Page i. That's the description page of the second round
in that piece and, although I can't read all of the details, it does look
as if it covers the Union Workhouse.
That doesn't help you find your man, but it might narrow it down so that
someone with access to the fiche would be able to search it for you. It
could be that the Workhouse inmates are only recorded by their initials, or
just that the writing is so bad that he's been mistranscribed. I'm
transcribing some Herefordshire parishes and it's very easy to get names
wrong.
If the Workhouse was fairly small, the inmates could all be listed on a
normal schedule number and therefore it won't appear as an institution
under the Institution search.
Best wishes,
Barbara Griffiths
Coventry UK