Yes it is regular..Let us see how :
We know modulo will lead to finite number of remainders here ranging from 0 to 4..Hence we can decompose the given language as :
L = L1 U L2........U L5
where L1 = bam | m is a multiple of 5 say 5k and hence 5k mod 5 = 0 and hence n = 0
Similarly L2 = abam | m = 5k + 1 and n = 1
and so on till L5..
As these are clearly regular..
So their union will also be regular..
Hence the given language is a regular language..