Ans- Yes, it can, if they are both placed according to vastu guidelines. For instance, south, South-east and west are considered ideal for kitchen placement. So if the Toilet is placed in SSW or ESE, and kitchen is in south or SE; they will be next to each other; but vastu shastra permits this arrangement.
Similarly, the WNW toilet and kitchen in west also placed adjacent to each other and yet does not violet any vastu rule.