This detachment's own printed rule ends with a restriction sentence: this detachment has the HEARTHGUARD tag and cannot be taken with another HEARTHGUARD detachment. The pack also prints UNIQUE: HEARTHGUARD as a banner above this detachment's heading, and that banner is the only one in the entire document.
The Munitorum Field Manual version 1.3 calls the tag something else. It reads UNIQUE: HEARTHBAND, and it lists that tag on both this detachment and Hearthband.
So two official Games Workshop documents print different names for the same tag. Following the rule this site applies everywhere, we assert the tag and we do not assert its name. We can still tell you the pair, because the two documents agree on it from different directions: the pack names one holder and forbids a second, and the Munitorum Field Manual names both. Neither points at a third detachment.
And here is the part that matters. It blocks nothing you could field.
Hearthband costs 3 Detachment Points. A Strike Force budget is roughly 3 DP, so Hearthband already consumes it entirely and cannot be combined with anything, tag or no tag. At Incursion you cannot afford Hearthband at all. The only pairing this tag could forbid is one the arithmetic already forbids.
That is the opposite of the equivalent situation in our Imperial Knights guide, where the two tagged detachments cost 1 DP and 2 DP, add up to exactly a Strike Force budget, and produce a genuinely illegal army that looks perfect. Do not carry that lesson across. This detachment pairs freely with all six 2 Detachment Point detachments and with both other 1 DP detachments.
Recommended pairings, all unambiguously legal:
Plus [Mercenary Oathband](/40k/armies/leagues-of-votann/detachments/mercenary-oathband) (2 DP, total 3). The Yield Point engine feeding Fury of the Hearth. This site has recommended the pairing since the faction was first published and it remains correct.
Plus [Needgaârd Oathband](/40k/armies/leagues-of-votann/detachments/needgaard-oathband) (2 DP, total 3). 1 Yield Point per enemy unit destroyed, spent straight back into Einhyr shooting.
Plus [Dêlve Assault Shift](/40k/armies/leagues-of-votann/detachments/delve-assault-shift) (2 DP, total 3). Two deep strike packages landing on the same turn.
Plus [Farseekers](/40k/armies/leagues-of-votann/detachments/farseekers) (1 DP, total 2). Recon in front of the anvil.