There is no compatibility issue between vendor as far as IP CLOS implementation is concerned. You can use Juniper as Spine and any other vendor as Leaf there should not be any problem. IP close is just L2 point to point connectivity between spine and leaf which is supported by all vendors.
For VXLAN implementation Juniper does support Manual VXLAN as well as VXLAN with EVPN as overlay. You can refer to the below doc for VXLAN implementation on Juniper.
https://www.juniper.net/documentation/en_US/junos/topics/topic-map/sdn-vxlan.html
if you are using VXLAN I would suggest to use EVPN as overlay as it is supported on all vendor platforms who support vxlan.
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