Does NetBSD support the Solaris filesystem?
Kinda. If Solaris 5 or later created a filesystem with access control lists (ACL), NetBSD’s fsck(8) will render the superblock unusable to Solaris (i.e. Solaris can’t mount the filesystem again). You should either mount your Solaris filesystem read-only or have created it without ACLs. See this post by Christos Zoulas on this topic.