Você não deveria ter que fazer nada de especial; Eu tenho exatamente a mesma configuração que você (várias VLANs roteadas por um par HA de caixas Linux usando keep-alive).
Vejo keepalived envia NAs não solicitados quando uma caixa recebe MASTER:
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Dec 18 12:03:29 fw1 Keepalived_vrrp[23646]: VRRP_Instance(ipv6) Sending Unsolicited Neighbour Adverts on bond0.11 for 2001:44b8:xxxx:xxxx::f0
Dec 18 12:03:29 fw1 Keepalived_vrrp[23646]: VRRP_Instance(ipv6) Sending Unsolicited Neighbour Adverts on bond0.12 for 2001:44b8:xxxx:xxxx::f0
Dec 18 12:03:29 fw1 Keepalived_vrrp[23646]: VRRP_Instance(ipv6) Sending Unsolicited Neighbour Adverts on bond0.14 for 2001:44b8:xxxx:xxxx::f0
Dec 18 12:03:29 fw1 Keepalived_vrrp[23646]: VRRP_Instance(ipv6) Sending Unsolicited Neighbour Adverts on bond0.15 for 2001:44b8:xxxx:xxxx::f0
Dec 18 12:03:29 fw1 Keepalived_vrrp[23646]: VRRP_Instance(ipv6) Sending Unsolicited Neighbour Adverts on bond0.16 for 2001:44b8:xxxx:xxxx::f0
Dec 18 12:03:29 fw1 Keepalived_vrrp[23646]: VRRP_Instance(ipv6) Sending Unsolicited Neighbour Adverts on bond0.18 for 2001:44b8:xxxx:xxxx::f0
Dec 18 12:03:29 fw1 Keepalived_vrrp[23646]: VRRP_Instance(ipv6) Sending Unsolicited Neighbour Adverts on bond0.19 for 2001:44b8:xxxx:xxxx::f0
<snip>