Most of OpenSolaris was under the CDDL, which provides protection from patent claims from Sun (now Oracle). So if you used OpenSolaris, they wouldn't have a case through copyright infringement -- it's an approved open-source license -- or through patents they hold. Reality is complicated, so it's always a good idea to read the license code is released under: http://www.opensource.org/licenses/cddl1.php
In other words: your concern about OpenSolaris specifically is unfounded. DalvikVM wasn't make by Sun and released under the CDDL, so there was no patent protection. This will still have a chilling effect on the Java ecosystem, of course.
In practice I would use Solaris for databases and storing other critical data. Linux has a long way to go before it has something as mature as ZFS, and I wouldn't trust important data on anything less. DTrace adds introspection that is wonderful on a live database as well. Operating systems are tools, so use them for what they're good at.