If we are measuring time complexity for one array can we disregard a different array in our time complexity calculation?
Yes, IFF the different array is of a constant size.
If the array in question is the only one that grows proportionally to the input size n, this implies, that the other array is of a constant size, and the constant factors are disregarded in the Asymptotic Analysis. So, you will end up with O(n) time complexity.
If, however, another array is not of a constant size and it changes according to the input size, then the corresponding correlation (how it changes based on the input) should be calculated and multiplied by T=O(n).
Note, that your wording:
If we are measuring time complexity for one array
is not quite correct, as you don't calculate the Time Complexity for an array, list, or any other data structure, per se; rather you calculate it for your algorithm, which might involve different data structures, constructs, and operations.