We're about to move a site from a parallel site collection into a subsite of the other site collection. Both SC's are in the same Web Application. We have not been able to get the command line version of Export-SPWeb to work (see: https://sharepoint.stackexchange.com/questions/16882/migrating-a-site-from-one-sc-to-another-contenttype-problems) but we have been able to get the Central Administration export site functionality to work. Unfortunately we can't enable UseSqlSnapshot because it's not an option on the web interface.
So my question is: does executing a Site Export from Central Administration lock the database for Writes AND Reads? or just Writes? And does sharepoint handle this gracefully?