Yes, a /30 is a perfectly valid option for any point-to-point network from router to router. If that network happens to be an IPsec tunnel, it's all the same. Of course you'll have to select a subnet and address that does not overlap with another one in your network.
Routers have been supporting /31 for quite a while - even if the first and last address in a /31 are network and broadcast address.
Usually, OSPF copes well with that, too.
Which addresses you choose for your point to point links is up to your addressing plan entirely.
Some admins prefer to pick an IP range entirely unrelated to any end system's IP subnets, and allocate their /30s and /31s, but also the /32s for the Loopback addresses from there. This has some benefits when traffic filtering at the network edge is meant to protect the routers; a filter configuration becomes pretty simple - just add a deny rule with the given IP range.
Personally (and this is now opinionated), I try to pick one larger block (say, a /18) for an entire IPv4 network of a given customer, large enough to cover all the customer's sites and leave some room to grow. Then I would allocate a suitable sub-range at the end or the beginning thereof (like, a /23), which is then split up as needed for transit networks, (typically some /28, leaving room for two or three tuples of HSRP/VRRP) and /30 or /31 for point-to-point and for Loopback (/32) addresses. This approach, when working with traceroutes, helps end system's admins, supporters and also the newby network admin to spot where traffic starts to leave the given customer's network. As long as the first-two-octets-and-some-more-digits of the IP addresses showing up in traceroute output remain the same as on their end systems, they can tell if traffic is still within the given customer's network or not.