give build.xsl:
<?xml version="1.0" encoding="UTF-8"?>
<project default="build" name="TestApp" basedir="." xmlns:build="build">
<target name="W"> <echo>WWWWW</echo> </target>
<target name="X"> <echo>XXXXX</echo> </target>
<target name="Y"> <echo>YYYYY</echo> </target>
<target name="Z" depends="X,W,Y"> <echo>ZZZZZ</echo> </target>
</project>

and build.gradle:
ant.importBuild 'build.xml'

running "ant Z"
X:
[echo] XXXXX
W:
[echo] WWWWW
Y:
[echo] YYYYY
Z:
[echo] ZZZZZ

running "gradle Z"
:W
[ant:echo] WWWWW
:X
[ant:echo] XXXXX
:Y
[ant:echo] YYYYY
:Z
[ant:echo] ZZZZZ

The Ant documentation explicitly defines that the dependency list should be processed in left to right order if there is not an explicit dependency topology: http://ant.apache.org/manual/targets.html#targets

It appears that Gradle is processing the list in alphabetical order.