Unix/Linux will ignore environment variables such as LD_LIBRARY_PATH, SHLIB_PATH and LIBPATH required for Oracle's Instant Client when called from a SUID binary (which APPX typically is). To accomodate this, you'll want to remove the SUID on appx and configure APPX Login Manager to impersonate the appx user (typically appx) and appx group (typically appxgrp). This is accomplished via the service .ini parameters:

ImpersonateGroup            = NamedGroup(appxgrp)               #[LogonUser, NamedGroup(groupname), ServiceOwner] 
ImpersonateUser             = NamedUser(appx)          #[LogonUser, NamedUser(username), ServiceOwner]

Connections via the APPX Login Manager will then be able to make use of the Oracle Instant Client connection. From the command line, you can connect to the APPX Login Manager via the -c argument to appx like so:

appx -c