XML Stack Overflow

Issue

1.) Is it possible to have multiple Site Map Indexes spread out over multiple hosts? 2.) I cannot find documentation for the syntax to reference a Site Map Index from another Site Map Index. Any ideas? (http://ift.tt/tW4ZOF didn't seem to have it) 3.) Will Google honor multiple robots.txt files, spread out over multiple hosts, pointing to various Site Map Indexes?

Setup

We have 2 applications hosted separately, but appearing under the same domain via our server configuration:

App One:

http://appone.com/ (ROOT)
http://ift.tt/1J9tlxv
http://ift.tt/1E30iMd
http://ift.tt/1J9tlxB
http://ift.tt/1J9tktr

App Two:

http://ift.tt/1J9tlxF (ROOT)
http://ift.tt/1J9tlNX
http://ift.tt/1E30kDC
http://ift.tt/1E30lHH
http://ift.tt/1J9tlO3
http://ift.tt/1E30kDE
http://ift.tt/1J9tkJY
http://ift.tt/1J9tkK7

Since each app is hosted separately, we've set up a robots.txt file in App Two to point to the sitemap index (per specifications: sitemaps.org) at the root of App One http://ift.tt/1E30iMd

Dynamic XML - App Two

The second application generates XML sitemaps dynamically, between 90,000 and 150,000 links (a handful of .xml sitemaps). Once that's determined, an XML sitemapindex is generated dynamically (dynamic_sitemap_index.xml) to point to these sitemaps.

Do you know if what I'm trying to achieve is possible or has any adverse effects on SEO?

Multiple robots.txt on multiple hosts

Declaring multiple sitemapindexes supposedly works in a single robots.txt file, (http://ift.tt/1J9tkKa) but what about multiple robots.txt files across multiple hosts?