Is it safe to do so?
It should be considered safe. For better privacy and security, using your own Electrum server in Bluewallet could also help. Creating transactions in a watch-only wallet using bluewallet and signing them using Electrum offline has no issues.
Is there any better way to do it so I don't have to send the unsigned and signed transaction ...
Looking at the BitGoJS code it would appear that the derivation path is m/0/0/derivationChain/*.
Looking further, the derivationChain seems to be a code depending on the address type:
[0, UnspentType.p2sh, Purpose.external],
[10, UnspentType.p2shP2wsh, Purpose.external],
[20, UnspentType.p2wsh, Purpose.external],
[1, UnspentType.p2sh, ...