Matched filters are indeed necessary to get the most sensitivity. However, in addition to the matched filter searches, LIGO performs "waveform agnostic" searche

Matched filters are indeed necessary to get the most sensitivity. However, in addition to the matched filter searches, LIGO performs "waveform agnostic" searches that will find a signal regardless of its waveform. However, these searches are necessarily less sensitive than the matched-filter searches. No unmodeled events have yet been detected.