Yes. If you want all the xubuntu themes and branding, install the xubuntu-artwork package. Note that this will install the Xubuntu 11.04 themes, if installed on Ubuntu 11.04, etc. (as the repositories all have the same version, regardless of which desktop environment you use).

Be aware that the Xubuntu themes are tested primarily in the XFCE environment: there may be gaps in the coverage when used in a GNOME environment, although it may also be that it works perfectly.

If you are especially attached to the Xubuntu 10.04 theme, and the theme in 11.04 is unsuitable for you, you could potentially forward-port the xubuntu-artwork (and dependency packages) in some private repository (e.g. a PPA). Note that there may be changes in the theming engines or similar that may affect the work of forward-porting these packages.