Chris, oil can leak out of the vent tube while the sled is up side down.
An Apex is set-up differently then the Nytros and Phazers. On an Apex the vent line is routed from the left front of the crankcase to the air box (on a stock sled) or on boosted sleds the hose can be routed down towards the belly pan. On boosted sleds, they have a long vent hose that may or may not have a filter on the end.
Most of the oil is in the tank, there is some oil in the bottom of the crankcase though. On an Apex it's the oil that is in the bottom of the crankcase that can leak out of the vent hose. The oil in the tank on an Apex is some what captured, because the hoses are routed to the engine, instead of the atmosphere (or air box) like on a Nytro/Phazer.
Nytros and Phazers will leak directly out of the oil tank.
A roll-over valve can be installed in the long vent line, or up on the engine where the vent attaches to the left front of the crankcase. To help prevent the oil that is in the crankcase from leaking out.
Also even with a roll-over valve installed on an Apex, you do not want to leave the sled upside down for an extended peroid of time. Since it is possible to get an air lock in the oil pump supply line. It is rare for this to happen however.