Vectra packet capture ports are entirely passive interfaces and do not generate any packets. For this reason the capture interfaces cannot participate in active link aggregation technologies such as LACP/802.3ad.
All capture interfaces accept all packets on any port without distinction and you may therefore aggregate the links without LACP by permanently enabling link aggregation. In Arista and Cisco configuration terminology this is referred to 'mode on' instead of 'mode active'.
When configuring link aggregation it's important to ensure that all packets for the same flow (TCP/UDP streams) arrive at the same sensor. Sensors will reassemble asymmetric flows arriving on different ports on the same sensor but cannot reassemble asymmetric flows where the two directions of traffic flow arrive separately on two (or more) sensors.