The 5x0 is using an (previously) unsupported chip, making it impossible to use the ethernet ports.
SFP ports would still work though.
Read Trying to install OpenWrt on a Velocloud 520-AC
I'd look at the Dell Edge E42W 6x0 series instead, but skip the 610 model, they're the same as the VEP14xx, but the 6x0 are a lot cheaper on eBay.
ref: https://japancatalog.dell.com/c/wp-content/uploads/SD_WAN_EDGE_600_spec_sheet.pdf