Yes, but only if the plan is confirmed in Crewing PAL. In LiveFleet, confirmed relievers can be made visible in the timeline by toggling the option "Include Planned Seafarers".
In LiveFleet, we only display seafarers that are currently on board the vessel, or for which the plan is confirmed. This is the equivalent of the green bars (Sail/Confirmed Plans) in Crewing PAL > Graphical Plan This means that if a plan is not ...