This is only, after we in this thread have errataed Guidelines for ReTe wards.
Hidden Shape for inner heartbeasts is anyway tricky even without such needs.
So what is more plausible:
(1) inner heartbeasts resisting like typical supernatural beings with Might 0,
(2) inner heartbeasts being easy to detect by Hermetic Magic, because they react like no other supernatural beings of their power,
(3) lots of powerful supernatural beings with no Might at all?
No. I am not using any proposed errata from this thread. Different forms have different guidelines for wards. I don't consider that an error.
(1) is obviously not true.
(3) is not true either. There are beings with magical powers that have no Might, but there aren't lots of them.
(2) is only partially true. It isn't necessarily easy to detect a heartbeast, but in some cases - like an Elemental Inner Heartbeast - the fact that it is obviously not a mundane creature, and is not a creature with Might, means the most likely explanation is that it is a human who has changed shape in some way. Not necessarily by way of heartbeast, but that is one possibility.
So, (2) and (3) are the most plausible of those, even if neither is fully true.
Note that beings with might, even Might 0, are markedly different from beings with no might.
Even setting aside the MR issue outlined by Troy, it also means you are immortal and don't suffer from warping.
If, say, you allow Ward guidelines against beings with Might to be applied with beings with no might, do you also allow rego vim control spells to work on them? And if not, why?
So, back to the OP, I'd say no to guidelines for beings with might, yes to guidelines for elemental material or animal.
Agreed with the fixer. I see Inner Heartbeasts as essentially heartbeasts with a non-warping permanent active spell effect. If you want to protect yourself from a fire bird, you protect yourself with ward against heat and flames.
And hope you have enough Penetration to keep it away.