Yes.  Since the ATP levels are precisely maintained in healthy cells, the level of ATP accurately reflects the number of viable cells in a culture. 
In response to a proliferative signal (e.g. a growth factor) the number of cells in a culture will increase and this is reflected in the increased ATP levels in that culture.  In this context, the ViaLight kits provide excellent end point determinations in bioassays of cytokines and other growth factors. 
Since ATP is lost when a cell dies, the same assay can be used for cytotoxicity testing.  Reduction in ATP levels in response to a toxic agent can be directly related to the toxicity of that substance.  Since the ViaLight kits are far more sensitive than other methods used in cell viability studies (e.g. MTT), very subtle cytotoxic effects can be detected which would otherwise be missed by alternative methods.