Are "fact sheets" an acceptable reference?
If they are summary statistics, where possible, it's better to cite the source report or dataset but in general it's reasonable to cite such fact sheets as a published document authored by either the named author(if named) or the department which has generated it. 

If the summary stats are published as part of a report cite the report, if they're just published as a web page then you'd cite it as a web page with retrieval date included. 

How strong a source they are depends on the fact and the source. For example, statements about population changes or similar on a web page published by the census bureau would be an extremely high quality source. 

On the other hand a snippet of general health advice without citations in a public brochure may be of far lower quality.