Is the limited camouflage on Seed-Soldiers optional like usual? (I assume it is). If it is, there's nothing preventing you from making one of your Seed-Soldiers your datatracker while they're in the Seed-Embryo state, right? Unless Seed-Embryo itself is a marker state?
It's Limited Camouflage, it works like Limited Camouflage. For the rest of the question, an answer to what Seed-Embryo is would require actually having 3rd edition rules for it instead of trying to guess how it works based on the 2nd edition rules.
seed-embryo is a marker state. dunno why you'd want a data tracker that can't move or defend itself for a turn anyways from the wiki: If the Seed-Embryo is discovered, replace the Camouflage Marker with a Seed-Embryo (SEED-EMBRYO) Marker.
Seed-Embryo Marker is a Marker and not a Model or miniature. Datatracker requires the trooper to be a Model, specifically. Pretty damned cut and dry, if you ask me. This could change only with a rules alteration, if you ask me.
They are deployed as camo, so they actually do start in a Marker state. Much like Seed Soldiers, actually.