On initial glance through the Ritual Spellcasting rules, I don't see anything that would prohibit casting an area spell. It makes sense that you could do so.
Quote p.184 SR4A (Ritual spellcasting)
"Ritual spellcasting works much like regular spellcasting, except that it is cast over a longer period of time and can affect targets outside the magician's visual range."
Quote p.185 SR4A (Casting a ritual spell)
"Ritual Spellcasting is carried out int he same manner as Spellcasting, except that the ritual requires twelve hours, minus the leader's Magic (min 1 hour). Ritual Spellcasting can be either a Success Test or an Opposed Test, depending on the spell in question and where the target can resists it (see Spells, p. 87)."
Quote p.160 SM (Choose Range)
"Area Effect: ... area spells affect all valid targets within an area of effect. Area spells cannot affect individuals who cannot be seen, even if they are within the area designated for the effect."
Italics mine. So as long as the targets can be seen by the spotter, it makes sense that the area effect would get everyone within the area. However, using only a material link (as per rules from SM) to target someone does not appear (at first glance) to be able to affect anyone nearby.