Mysql database replication on different vlan/subnet/another site
Being asynchronous, replication works very well across WANs or otherwise remote locations. I have used such topologies many times in the past (e.g. replication from West Coast to East Coast, from US to Middle East etc.).

Just as with normal replication, but somewhat more obvious, you must watch for slave lag if you intend to read from slave and you must have the very latest data updated. Due to latency, bandwidth issues etc. you may find that your remote slave tends to lag more than a local slave. This doesn't have to be the case and I have witnessed remote slaves keeping up just fine with the master.

If you're using a VPN, there's nothing special about setting up this kind of replication. Otherwise, please consider using replication with SSL, so that your traffic is encrypted.