The FAG template isn't recommended, but it is not excluded from use. In fact, the Data Doctors project (which I am a member), has recently revived the usage of the FAG template (from what I've been told this was a leadership decision). This has caused a lot of confusion and misuse of the template itself.
WikiTree standards are that all sources be cited and that they follow the Evidence Explained standard.
https://www.wikitree.com/wiki/Help:Sources_Style_Guide
The template is intended to provide a way to create a hyperlink to a memorial page without direct copying and pasting the URL from the location bar of your browser. Either way, this doesn't follow EE standards.
A proper citation should never have a direct link to the source material because of the ever changing nature of websites. The FAG template transfers the effort of maintaining URLs from WikiTree members to the Data Doctor leaders. But again, it is not necessary if someone has cited their FAG source properly.
The misuse of the FAG template is a bigger problem than the simpliest use of the template (and even the instruction page for the template encourages the misuse). If someone uses the template only to create a hyperlink to the memorial page, then it could be part of an EE style citation.
So, for example. here is a FAG citation example from the EE forums where someone asked how to properly cite FAG:
https://www.evidenceexplained.com/content/find-grave
Find A Grave, database and images (http://findagrave.com : accessed 14 March 2011), memorial page for Claudia J. Esselstyn (1861–1862), Find A Grave Memorial no.7,487,109, citing Aztalan Cemetery, Milford, Jefferson County, Wisconsin; the accompanying photographs by Mike [--?--] and Kari Waterbury are materially informative, but do not provide a legible image of the inscribed data.
Here is the same example with Wiki markup:
<ref>''Find A Grave'', database and images (http://findagrave.com : accessed 14 March 2011), memorial page for Claudia J. Esselstyn (1861–1862), Find A Grave Memorial No. 7487109, citing Aztalan Cemetery, Milford, Jefferson County, Wisconsin; the accompanying photographs by Mike [--?--] and Kari Waterbury are materially informative, but do not provide a legible image of the inscribed data.</ref>
Above, I have also modified the memorial number to remove the commas to make the number more internationally friendly as not every language puts the commas in numbers the same way we do in English (not every language uses commas!)
Now, if you wanted to use the FAG template in a citation as above, which I do not, then you could do this:
<ref>''Find A Grave'', database and images (http://findagrave.com : accessed 14 March 2011), memorial page for Claudia J. Esselstyn (1861–1862), Find A Grave Memorial No. {{FindAGrave|7487109}}, citing Aztalan Cemetery, Milford, Jefferson County, Wisconsin; the accompanying photographs by Mike [--?--] and Kari Waterbury are materially informative, but do not provide a legible image of the inscribed data.</ref>
This would be the only usage that, in my opinion, would be tolerable give the conflicting standards of following EE and the Data Doctors usage of the FAG template. Anything else would not be following EE standards.
Why does EE not allow for adding links directly to material? For the very reason why Data Doctors decided to re-introduce the template, URLs are ever changing on the World Wide Web! While even the EE standard assumes that a domain name (the wikitree in www.wikitree.com) will never change, the reality is that can and does also change. But more common is that the content of a website often changes and URLs are fleeting. All citations to a website should only provide the URL of the domain (www.findagrave.com) and then enough information for any other genealogist to find the information themselves.
The reproducibility of a source is part of the EE and the Genealogy Proof Standard. Meaning, if you put a source citation on the profile of your 2x great-grandmother, and I read the citation, I should be able to go to the URL (or find it if it's changed) and use the information in the citation to find the data you found, today, tomorrow, in fifty years (or whatever you feel is reasonable).
So, with regards to FAG, does a source citation provide enough information, that you could go to www.findagrave.com and find the memorial page (using their search function). Try it!
EDITED: Removed extra white space.