Is it safe to say that you're still likely to be asked for the source of these funds even when they can see the funds has been moved from a dormant address?
They may not be asking or it totally depends on the platform we are about to deposit. But as an user we should be always be ready to provide the source of funds since the platform mention in their ToS while registering and failing to do will give them the upper hand and lock the funds indefinitely.
But the chances are less when the fund you are deposit matches the usual deposit and just split between multiple can reduce it further but better to go with decentralized no KYC option if it is possible.