Generally speaking asymmetric routing is fine. I am surprised it wasn’t happening more than it does on the ctwug network, considering how many different admins we have on the network and everyone not following the same rules on which ospf cost number to apply on interface.
Its actually a good idea, to always make sure we disable reverse path filtering on all linux machines on the network that does routing, eg. the tunnel servers. Since there is no specific reason to force symmetric traffic.
The only times I had to make sure traffic route symmetrically, is when you work with firewall devices, or DPI devices that need to see both directions of a TCP conversation.
ps. On the internet you will find almost all traffic that routes to different geological locations are almost always routed asymmetrically.