Jacqueline, yes you are correct that Hicks Yews were used as a background hedge in this garden. Hicks Yews are typically sold in the 24" - 42" sizes, but some nurseries sell ones as tall as 72". There are also taller Yew options such as Taxus cuspitata 'Fastigiata', Taxus cuspitata 'Adam's' or Taxus cuspitata 'Capitata Natural' that could be purchased as tall as 7'-8'. These will become trees and a possible alternative to Hemlocks. However, unlike Hemlocks, Yews are not deer resistant. Good luck.