But I am not interested in any seed, I am interested only in the seed created by KeepKey hardware wallet. For that to be verified a transaction should somehow be present both on the Electrum-Keep-Key hot wallet and the cold wallet generated from the Keep-key seed and this is apparently impossible to do.
If by "present" you mean showing up on your other wallet while it is offline and not connected over the internet to update your balance, then I don't think that is true. In most cold-wallet setups you would use the watch-only/hot-wallet to check your balance with the block explorer and so on. As mentioned above, if the address are the same and you use the same seed then it is guaranteed to show up regardless of what wallet you use as long as they use the same derivation path. CMIIW.