When are games against engines drawn? When two engines play against each other in a game of chess, when is it appropriate to declare a draw when clearly no progress is possible?

For example:
8/6k1/8/R3K2p/2r3p1/6P1/7P/8 w - - 0 2

This was a position reached against two engines I am having compete. It has been going on for a while and I doubt a win is possible. Repetition seems like a while away, and I think the fifty-move rule only works if a player requests for it (these engines don't do that). I can't even declare this a draw by endgame tablebases because it has 8 pieces.
Try the TCEC adjudication rules, adapted for your situation. You can use more aggressive (or less aggressive) adjudication rules if you need them, e.g. by changing the threshold eval needed for adjudication.
Win adjudication:

Game ends in a win if there is a mate, engine resigns, time runs out, there is a crash, illegal move, by 6-men TB adjudication, or by the TCEC winrule: both playing engines have an eval of at least 10.00 pawns (or -10.00 in case of a black win) for 5 consecutive moves, or 10 plies - this 10/10 rule is in effect as soon as the game starts. In the website this rule is shown as &quot;TCEC win rule&quot; with a number indicating how many plies there are left until it kicks in.

Draw adjudication:

A game can end in a draw by three-fold repetition, 50-move rule, stalemate, 6-men TB adjudication, and the &quot;TCEC draw rule&quot; (ending the game at move 35 or later if the evals from both playing engines are in [-0.15, +0.15] for 10 plies without a pawn advance or any capture).