Are you talking in Bayesian sense or Frequentistic sense? If the latter, then it is not logical as 'absent' and 'no data' is clearly not the same. However, if there are some probability that data deficient taxon will be threatened then the weight can be somewhat similar.

'Data deficient' based on IUCN's definition. 'Data Deficient' species has insufficient information for a proper assessment of conservation status to be made.It doesn't necessarily indicate that the species has not been extensively studied but it may indicate that little or no information is available on the abundance and distribution of the species. But careful consideration of 'data deficient' species because 'absence' may indicate severe low abundance. So, perhaps, in some cases, it is sensible to consider some 'data deficient' species as 'Threatened'.