Appears influxDB currently has support for just 1 typesdb file. Those who maintain custom types.db files for their collectd implementations will have to merge types.db's into 1 file if they use "Type" from both.

Reproduce:
[input_plugins.collectd]
enabled = true
port = 25826
database = "collectd"
typesdb = "/usr/share/collectd/types.db.custom"
typesdb = "/usr/share/collectd/types.db"

/opt/influxdb/current/influxdb -config /opt/influxdb/shared/config.toml
Couldn't parse configuration file: /opt/influxdb/shared/config.toml
[11/10/14 15:13:00] [INFO] Loading configuration file /opt/influxdb/shared/config.toml
Near line 57, key 'input_plugins.collectd.typesdb': Key 'input_plugins.collectd.typesdb' has already been defined.

or similarly (using space or , as separator)
[input_plugins.collectd]
enabled = true
port = 25826
database = "collectd"
typesdb = "/usr/share/collectd/types.db.custom" "/usr/share/collectd/types.db"

/opt/influxdb/current/influxdb -config /opt/influxdb/shared/config.toml
Couldn't parse configuration file: /opt/influxdb/shared/config.toml
[11/10/14 15:14:22] [INFO] Loading configuration file /opt/influxdb/shared/config.toml
Near line 56, key 'input_plugins.collectd': Near line 56: Expected a top-level item to end with a new line, comment or EOF, but got '"' instead.

Could we support multiple to align with collectd?