VyOS 1.1.8 allows IKE DPD interval from 15 to 86400 sec and timeout from 30 to 86400 sec, default values of 30 and 120 sec, are incompatible with Cisco ASA which has DPD interval from 2 to 10 sec and timeout from 10 to 3600 sec with 2/10 sec by default.
Possible workaround is to use 10/30 sec on Cisco and 15/30 sec on VyOS with slow dead-peer-detection and slow failover.
Hope we could adjust these values.