Does F5 DNS Supports Juniper Lightweight LB?

Add it as a generic host server type and make the VIP to be same as the server IP address but just with a port and use not big ip monitor (so you configure generic host with ip 1.1.1.1 and add VIP with IP address 1.1.1.1 : 80 and another VIP with 1.1.1.1:443). Maybe tcp or tcp half open for the server and for example HTTP for the VIP virtual server. Be carefull which F5 device will send the probes so if you create a separate data center object for the Juniper and there is no F5 device in the same data center that has connectivity to the Juniper then better use prober pool and make certain which F5 device have network and security access to send the probes and tell the GTM/DNS that the Generic host is ok.

https://techdocs.f5.com/kb/en-us/products/big-ip-dns/manuals/product/bigip-dns-concepts-12-0-0/5.html

If the Juniper Lightweight LB has more than one VIP servers also with different IP addresses you can try the type "Generic Load Balancer" but it uses SNMP for the server monitor and I have never seen anyone use this type at all:

https://devcentral.f5.com/s/question/0D51T00006i7hJM/gtm-load-balancing-generic-load-balancers