Not legal to cross foul line at any time, what happen was a couple of pairs the foul lights malfunctions they had to be cut-off so, they have to turn them off on all lanes by rule.

I bowled travel league this weekend, and was in a center that the foul lines did not work. there were balls being rolled and feet all over the lines. was wondering if this is legal?

Balls rolling across the foul line are not fouls.
Feet crossing is a foul though.

5a/4 Is a foul called when the ball rolls over the foul line during delivery and the foul detector
is activated?
The bowling ball is not considered a part of the bowler’s body. If the bowler did not step on or
go beyond the foul line, a foul is not recorded.

Commonly Asked Question – Rule 5c.
5c/1 What happens if our foul lights are not available?
If not available, members of the league should be advised the captains are responsible for the calling of fouls or someone can be designated to act as a foul judge.

And it's not just the feet, any part of your body that touches anything beyond the foul line is a foul.  This includes touching the wall beyond the foul line on an end lane.  Many centers draw a "foul line" on the walls to make that clear.