TBH, I think that kinda makes more sense than Willpower + Sleaze. Its an effect of the devices being inside the host, and spotting them from outside should be hard regardless of a Spider being present. Intuitively, Device Raing + Sleaze that would have been my take as well.
That being said: Boy, the Attributes used for the different Matrix Actions really are all over the place, aren´t they? There´s no way of intuitively knowing what values are used under what circumstances. Sometimes its Firewall, but sometimes also Sleaze, Data Processing or Device/Host/Pilot Rating or even Attack, and most of the times there are multiple alternative defense tests against (presumably) Personas and Spider-protected hosts using any of the 4 mental Attributes. And to that, you have to add different Access Levels, Legality, Linked Matrix Attributes and Action Types. So much for Simplificition, it´s practically unusable without a flip-chart. Fragg, why can´t we just have Matrix rules that aren´t overly complicated?