Convert %ArrayOfDataTypes to array, and back again

There isn't a built-in method that does exactly what you're looking for, that I know of. Here's a simple example of how to do it, though:

Class DC.Demo.ArrayUtils
{

ClassMethod ArrayObjectToArray(pSource As %Collection.AbstractArray, Output pTarget)
{
    Kill pTarget
    
    Set tKey = ""
    For {
        Set tItem = pSource.GetNext(.tKey)
        Quit:tKey=""
        Set pTarget(tKey) = tItem
    }
}

ClassMethod ArrayToArrayObject(ByRef pSource, pTarget As %Collection.AbstractArray)
{
    // Could initialize pTarget here and return it Output, or return it normally.
    // This is just a bit more general because it'll work with any array collection type.
    Do pTarget.Clear()
    
    Set tKey = ""
    For {
        Set tKey = $Order(pSource(tKey),1,tItem)
        Quit:tKey=""
        Do pTarget.SetAt(tItem,tKey)
    }
}

}

Usage:

USER>s aodt=##class(%ArrayOfDataTypes).%New()
 
USER>w aodt.SetAt("lcavanaugh","username")
1
USER>w aodt.SetAt("organization","coolcompany")
1
USER>zw aodt
aodt=<OBJECT REFERENCE>[1@%Library.ArrayOfDataTypes]
+----------------- general information ---------------
|      oref value: 1
|      class name: %Library.ArrayOfDataTypes
| reference count: 2
+----------------- attribute values ------------------
|Data("coolcompany") = "organization"
|   Data("username") = "lcavanaugh"
|        ElementType = "%String"
+-----------------------------------------------------
 
USER>do ##class(DC.Demo.ArrayUtils).ArrayObjectToArray(aodt,.array)
 
USER>zw array
array("coolcompany")="organization"
array("username")="lcavanaugh"
 
USER>s newaodt = ##class(%Library.ArrayOfDataTypes).%New()
 
USER>do ##class(DC.Demo.ArrayUtils).ArrayToArrayObject(.array,newaodt)
 
USER>zw newaodt
newaodt=<OBJECT REFERENCE>[2@%Library.ArrayOfDataTypes]
+----------------- general information ---------------
|      oref value: 2
|      class name: %Library.ArrayOfDataTypes
| reference count: 2
+----------------- attribute values ------------------
|Data("coolcompany") = "organization"
|   Data("username") = "lcavanaugh"
|        ElementType = "%String"
+-----------------------------------------------------

If you really wanted to make BuildValueArray work:

USER>d aodt.%SerializeObject(.serial)
 
USER>d aodt.BuildValueArray($lg(serial),.anotherarray)
 
USER>zw anotherarray
anotherarray("coolcompany")="organization"
anotherarray("username")="lcavanaugh"

The utility method approach would probably at least be clearer.