I think an answer to this depends on what year in the war we are talking about. In 1915 they did look "Russian-ish" but with enough differences (as has already been pointed out) that Russian figures won't work:

Towards the war's end, their uniforms had more German elements, but again, with enough differences that German figures won't do:
Note that this type of helmet is not represented (yet) in 1/72 plastic.

Well, I did intend to keep
my reply short in the last two sentences. Now I see that it might be read as condescending, wich was not the intention, and I appologize
if it was read as such. I just wanted to say that it is a personal choice on deciding what compromises you are willing to do when accepting a figure in your army. I had worked on a russian WW I army, where besides Hat (not at all
happy with missing bayonets on rifles), Zvezda and Strelets, the horrible Redbox Boxer uprising russians are also serving in infantry, with painted peaks where there are not any. But the Redbox set works for me, the peak on the cap
was so small anyway, that even at close look they are ok for WW I painted accordingly. The Zvezda infantry will do more duty in WW II as border guards and NKVD troops along the Zvezda dedicated set. I did look into painting Hat russians as bulgarians, but the major obstacle was the gimnastiorka. Thus your reply, discouraging Strelets from making a dedicated set of bulgarians, did frustrate a couple of the fellow contributers on this forum.

Many thanks for taking the time to post this here PDA. Info on the Bulgarians is quite scarce, and sadly missing from the overview at Landhips:
http://www.landships.info/landships/uniform_articles.html#

Agreed it is a matter of personal taste which compromise to do, or not.

Re: the Russians, mine are nearly complete. I added some bayonets where I could. The Zvezda are stunning as concerns detail and poses, but there is a problem where I for one don't compromise, and that is scale. For my personal taste (add as many exclamation marks here as needed) they are too tall. The Redbox have also been drafted and I would like to add the blanket/coat rolls over their shoulders but probably won't bother. Shallow detail but at least the right scale for me.

Re: my reply, I was asking a simple question for information and it would be definitely overrating my influence on Strelets to state this made them decide in one way or another. If Strelets can see the differences from the info posted here it will help them to decide. So you and PDA have helped by providing info.

Again in my personal view, the Balkans are much underrated as a WW1 theater in the West, so I hope a manufacturer from the East does those armies justice. Regards, Pa