There are AHL-level contracts that don't count against a team's cap/50-contract limit/etc. But keep in mind that a lot of prospects have deadlines on how long their rights can be held without signing an ELC (for example: players drafted from the CHL have to be signed within two years of their draft date, players drafted from the NCAA have to be signed by the middle of August after their class graduates (which doesn't necessarily mean they have to graduate/finish their four years)).
Matt Auffrey might be a good example of a player from the NCAA who was drafted, then opted to make the jump to the OHL and then had a year of AHL (with an AHL contract) where Anaheim still owned his rights, but didn't have to sign him to an ELC.
In Orlov's case, he'll likely be signed by the Capitals in the offseason, they just didn't want to burn a year of his ELC for this short period of time while he finishes off the season in Hershey (there might also be waiver considerations there, but I am unsure).