Being married to a BT, I can speak from experience. I am fortunate that my husband is a wonderful, loving, chessed filled man, from whom most frum people could learn a thing or two about menschlechkeit. That said, it has not always been an easy ride. My dad O”H really missed having a mechutan with whom he had Torah in common, who would have understood and appreciated the Divrei Torah my father said over at the Sheva Brachos, and many other similar occasions, like brissim, Bar-Mitzvahs,etc. My parents and my in-laws got along really beautifully, but it was a very superficial, pleasant relationship, because the only thing they had in common was us and the grandchildren (which is true for many both-sides-frum machetonim).
It IS difficult when one side is completely frei, unless every single member of that side has total respect for the religious couple. We got into trouble when family members married “out,” and there were hard feelings on their part when we did not attend their celebrations. I davened for only female children to be born to those relatives, so that at least the grandchildren’s children would be assured of being Jewish (and B”H so it was).
Personally, I believe it is easier for two BT to marry and grow together in their learning and Yiddishkeit, but that should not stop someone from redting a shidduch with someone who is FIRMLY entrenched in Yiddishkeit. Someone who is newly frum is another story, to me. I would want to see the level of their commitment, first. I have seen people flip in and flip out, and I have seen BT FRUM relatives who married into my family, who divorced, and then became frei again. This is not an easy question to answer.
No one who is sincere, should be “barred” from good shidduchim, but unquestionably one has to use seichel when redting to them.